This St. Patrick’s Day cake is an eye-catching, top hat-shaped rainbow cake with a surprise Lucky Charms marshmallow center! While it may look elaborate, it’s actually easy to assemble once the layers are baked. Featuring vibrant rainbow layers and a festive green buttercream frosting, this cake will be the star of your St. Patrick’s Day party!

Full Recipe:

Ingredients

Cake

Cooking spray
5 1/2 cups (660 g) all-purpose flour
1 tbsp baking powder
1 tsp kosher salt
3 cups (600 g) granulated sugar
1 cup (2 sticks) unsalted butter, softened
1 cup vegetable oil
6 large eggs
1 tbsp pure vanilla extract
1 cup whole milk
1 cup sour cream
Red, orange, yellow, green, blue, and purple food coloring

Frosting & Assembly

8 cups (920 g) powdered sugar
2 1/2 cups (5 sticks) unsalted butter, softened
1/3 cup heavy cream
2 tsp pure vanilla extract
1/4 tsp kosher salt
1 1/2 cups Lucky Charms marshmallows
Green, black, and yellow food coloring

Directions

Cake

Step 1
Preheat oven to 350°F (175°C). Line one 8-inch cake pan and five 6-inch cake pans with parchment paper and coat with cooking spray. In a large bowl, whisk together flour, baking powder, and salt.

Step 2
In another large bowl, use a handheld mixer to beat the granulated sugar and butter until combined. Add the vegetable oil and mix until smooth. Add eggs one at a time, mixing well after each addition, then beat in the vanilla extract.

Step 3
Gradually add the dry ingredients to the wet ingredients, alternating with the milk and sour cream, and mix until fully combined.

Step 4
Divide the batter into six bowls and dye each one a different rainbow color (red, orange, yellow, green, blue, purple).

Step 5
Pour the purple batter into the 8-inch cake pan and bake for 15–18 minutes. Pour the remaining colored batters into the 6-inch cake pans and bake for 30–35 minutes. Let the cakes cool completely.

Frosting & Assembly

Step 1
In a large bowl, beat together the powdered sugar and butter until smooth. Add the heavy cream, vanilla, and salt, and mix until fluffy.

Step 2
Trim the tops of the cooled cakes as needed. Using a 3-inch round cookie cutter, cut out the center of the orange, yellow, green, and blue cake layers to create a hollow space for the marshmallows.

Step 3
Stack the cake layers in this order: purple (base), blue, green, yellow, and orange, adding a thin layer of buttercream between each. Fill the center hole with Lucky Charms marshmallows and top with the red cake layer.

Step 4
Frost the entire cake with a thin crumb coat of buttercream and refrigerate for 30 minutes.

Step 5
Dye the remaining frosting green and frost the outside of the cake until smooth.

Step 6
Separate 1 1/2 cups of frosting, dye 1 cup black and 1/2 cup yellow. Create a black belt design at the base of the cake and pipe a yellow buckle for a festive St. Patrick’s Day touch!

Nutrients (Per Serving, Approximate)

Calories: ~450 kcal
Protein: ~5g
Carbohydrates: ~65g
Fat: ~20g
Sugar: ~50g
Sodium: ~250mg

Why This Cake is Perfect for St. Patrick’s Day

Eye-Catching Presentation: The bold rainbow layers and green frosting create a visually stunning cake that embodies the festive spirit of St. Patrick’s Day.
Hidden Surprise Inside: Cutting into the cake reveals a fun cascade of Lucky Charms marshmallows, making it a delightful treat for kids and adults alike.
Rich, Moist Cake Layers: Made with sour cream and whole milk, the cake layers are fluffy, tender, and full of flavor.
Smooth and Creamy Buttercream Frosting: The luscious buttercream not only provides a delicious taste but also ensures a smooth, polished finish for decorating.
Easy to Customize: You can switch up the colors, fillings, or decorations to personalize the cake however you like.

The Magic of Rainbow Cake Layers

The base of this cake consists of six layers, each dyed a different color of the rainbow—red, orange, yellow, green, blue, and purple. Using food coloring ensures vibrant, distinct layers that pop when the cake is sliced.

Best Food Coloring to Use: Gel food coloring is the best choice for this cake, as it provides intense color without altering the texture of the batter.
How to Achieve Even Layers: Weigh the batter to ensure each layer is evenly divided before baking. This results in a uniform and balanced cake.
Preventing Color Bleeding: Bake each colored layer separately to avoid colors mixing together.

Creating the Hidden Marshmallow Surprise

A standout feature of this cake is the surprise marshmallow filling. By hollowing out the center of some of the cake layers and filling it with Lucky Charms marshmallows, you create a piñata-style cake that spills out colorful surprises when sliced.

How to Create the Hidden Center: Use a round cookie cutter or a knife to cut out the centers of the orange, yellow, green, and blue layers before stacking them. This leaves space to fill with marshmallows.
Best Fillings for the Surprise Effect: While Lucky Charms marshmallows add a fun St. Patrick’s Day touch, you can also use M&M’s, sprinkles, or small chocolate candies for a different surprise filling.

Buttercream Frosting – The Key to a Smooth Finish

The frosting for this cake is a classic buttercream made with powdered sugar, butter, heavy cream, vanilla extract, and a pinch of salt. This frosting is rich and creamy, making it perfect for both filling the layers and decorating the outside of the cake.

How to Get a Smooth Finish: Apply a crumb coat—a thin layer of frosting that seals in crumbs—before adding the final coat of green frosting. Refrigerating the cake between frosting layers helps achieve a clean, polished look.
Coloring the Frosting: Use green gel food coloring to create a vibrant, St. Patrick’s Day-inspired shade. For the hat details, separate some of the frosting and color it black for the belt and yellow for the buckle.
Piping Decorations: A piping bag with a small round tip makes it easy to create precise belt and buckle designs. If you don’t have a piping bag, a resealable plastic bag with the corner snipped off works as a substitute.

Assembling the Cake for the Best Structure

Since this cake is taller than a standard layer cake, proper stacking and stability are essential.

Use Cake Dowels or Straws: If the cake feels unstable, inserting a few straws or cake dowels through the center can help support the layers.
Chill Before Frosting: Let the stacked cake chill in the refrigerator for about 30 minutes before applying the final coat of frosting. This makes it easier to work with and prevents the layers from shifting.
Trim Layers for an Even Top: If the cake layers are slightly domed after baking, trim them flat before assembling to ensure a level top.

Fun Ways to Decorate and Customize the Cake

This cake is already a showstopper, but there are plenty of ways to make it even more festive:

Gold Sprinkles or Edible Glitter: Add a touch of shimmer to the frosting for a magical, leprechaun-inspired effect.
Chocolate Coins: Place chocolate gold coins around the base of the cake for an extra St. Patrick’s Day touch.
Edible Shamrocks: Pipe small shamrock shapes onto the cake using green frosting or place edible shamrock decorations on top.
Leprechaun Hat Cake Topper: A small fondant or paper leprechaun hat can serve as a playful cake topper.

Best Occasions to Serve This Cake

While this cake is perfect for St. Patrick’s Day, its bright colors and fun presentation make it a great choice for other occasions as well.

Birthday Parties: A rainbow-themed party wouldn’t be complete without a colorful cake like this.
Pride Celebrations: The rainbow layers make it a fantastic dessert for Pride events.
Unicorn or Fantasy-Themed Parties: Pairing this cake with whimsical decorations can make it fit any magical theme.
School or Office Celebrations: If you need a festive dessert to share, this cake will definitely impress a crowd.

How to Store and Keep the Cake Fresh

Since this cake is made with buttercream frosting and a marshmallow center, proper storage ensures it stays fresh and delicious.

Room Temperature: If serving within a few hours, keep the cake at room temperature in a cool place.
Refrigeration: Store in an airtight container in the refrigerator for up to 3 days. Let it come to room temperature before serving for the best texture.
Freezing: The unfrosted cake layers can be wrapped in plastic wrap and frozen for up to 1 month. Thaw before assembling and decorating.

Tips for Making This Cake Successfully

Use Parchment Paper: Lining the cake pans with parchment ensures easy release and prevents sticking.
Don’t Overmix the Batter: Overmixing can make the cake dense instead of light and fluffy.
Allow Cakes to Fully Cool: Frosting a warm cake can cause the buttercream to melt and slide off.
Adjust Baking Times as Needed: Different oven temperatures and pan sizes may require slight baking time adjustments—check for doneness with a toothpick.

Conclusion

This St. Patrick’s Day top hat cake is more than just a dessert—it’s an experience! From its bold rainbow layers to its surprise marshmallow center, every slice is filled with festive fun and delicious flavor. The smooth buttercream frosting, combined with the vibrant colors and creative decorations, makes this cake a true showstopper.

Whether you’re hosting a party, celebrating with family, or simply looking for a fun baking project, this cake is sure to bring joy and excitement to any occasion. With easy-to-follow steps and plenty of ways to customize it, this St. Patrick’s Day cake is a must-try for anyone who loves a festive and flavorful dessert. Enjoy every colorful, sweet, and lucky bite!

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