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Celebrate St. Patrick’s Day with this show-stopping top hat-shaped rainbow cake filled with a surprise center of Lucky Charm marshmallows. It’s a festive treat that combines vibrant colors and a fun twist inside, perfect for impressing friends and family. While it takes some time to prepare, the layering and decorating process is straightforward and rewarding. The cake layers include a special thinner rim to mimic the brim of a hat, and the leftover cake scraps turn into delightful cake balls that make for a perfect side snack.
I first made this cake last year when hosting a family party and was amazed at how everyone loved both the look and the flavors. It quickly became a highlight that everyone asks for again.
Ingredients
- Cooking spray: easy pan release
- All-purpose flour: structure
- Baking powder: ensure a light and airy texture
- Kosher salt: balance sweetness
- Granulated sugar: sweetness and tender crumb
- Unsalted butter: richness and moisture
- Vegetable oil: keep the cake moist
- Large eggs: binding and lifting the batter
- Pure vanilla extract: depth to the flavor
- Whole milk: moisture and tenderness
- Sour cream: a moist texture and slight tang
- Food coloring: red, orange, yellow, green, blue, and purple for the rainbow effect
- Powdered sugar: smooth frosting
- Unsalted butter: for creamy frosting
- Heavy cream: achieve the perfect frosting consistency
- Pure vanilla extract: flavor in the frosting
- Kosher salt: the sweetness of the frosting
- Lucky Charm marshmallows: the surprise inside
- Green, black, and yellow food coloring: decorating the hat embellishments
Step-by-Step Instructions
- Preheat the Oven:
- Preheat your oven to 350 degrees Fahrenheit. Prepare one 8-inch cake pan and five 6-inch cake pans by lining them with parchment paper and coating with cooking spray. In a large bowl, whisk together flour, baking powder, and salt. This is your dry ingredient base.
- Mix the Batter:
- Using a handheld mixer on medium high, cream the granulated sugar and butter until combined. Add vegetable oil and beat until the mixture is smooth and creamy. Incorporate the eggs one at a time, beating well after each addition, then add vanilla extract.
- Combine Wet and Dry Ingredients:
- Add about one third of the dry ingredients to the wet mixture and beat on medium low just until a few dry streaks remain. Pour in the milk and beat until combined. Add another one third of the dry ingredients and beat on medium low again until just streaks remain. Stir in the sour cream until incorporated. Fold in the remaining dry ingredients until just combined to keep the batter light.
- Color the Batter:
- Divide the batter evenly into six bowls. Dye one bowl of batter each red, orange, yellow, green, blue, and purple to create layers of the rainbow.
- Bake the Cake Layers:
- Pour the purple batter into the 8-inch pan to create the hat’s brim, which should be thinner than the other layers. Bake for 15 to 18 minutes, or until a toothpick inserted comes out clean. Let cool.
- Bake Rainbow Layers:
- Pour each of the remaining colors into the prepared 6-inch pans. Bake these for 30 to 35 minutes until a toothpick inserted comes out clean. Allow them to cool completely.
- Make the Frosting:
- In a large bowl using a handheld mixer on medium speed, beat powdered sugar and butter until smooth. Add the heavy cream, vanilla, and salt, and beat until fully combined and fluffy.
- Trim and Cut Centers Out of Cakes:
- Once cooled, trim the tops of cakes if needed to level them. Using a 3-inch round cookie cutter, carefully cut out the centers of orange, yellow, green, and blue layers. Save the centers for cake balls.
- Assemble the Cake:
- Place the purple layer on your cake stand or plate as the brim of the hat. Spread a thin layer of buttercream on top. Add the blue layer, then frost and repeat with green, yellow, and orange layers in that order, frosting the top of the orange layer. Fill the hollowed center with Lucky Charm marshmallows. Add the red layer on top.
- Crumb Coat and Chill:
- Frost the top and outside of the entire cake with a thin crumb coat of buttercream. Refrigerate for at least 30 minutes to firm up the frosting.
- Decorate the Hat:
- Dye about one and a half cups of buttercream green. Using an offset spatula and a bench scraper, cover the cake smoothing the green frosting all over the cake. Divide remaining frosting into one cup and a half cup. Dye one portion black and the other yellow.
- Create the Hat Band and Buckle:
- With the black frosting, frost a one-inch thick band across the base of the hat above the brim, using parchment paper to keep lines neat. Pipe a yellow buckle onto the black band using a piping bag fitted with a medium round tip.
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My favorite part of this recipe is the marshmallow surprise inside. When my kids discover it, their faces light up with pure joy. It really turns a festive cake into a magical experience.
Storage Tips
Store this cake covered in the refrigerator to keep it fresh and the marshmallows from melting too much. Leftover cake balls can be stored in an airtight container at room temperature or refrigerated. The cake layers freeze well individually if wrapped tightly in plastic wrap and foil, making advance prep possible.
Ingredient Substitutions
You can replace vegetable oil with melted coconut oil for a slightly different flavor and a dairy-free twist if you substitute the butter with a plant-based alternative. For the milk, use your preferred non-dairy milk but it may slightly alter texture. Sour cream can be replaced with plain Greek yogurt for similar moisture and tang.
Serving Suggestions
Serve this cake at your St. Patrick’s Day party alongside traditional dishes like corned beef and cabbage or Irish soda bread for a full festive meal. A cup of strong black tea or coffee pairs beautifully with the buttery sweet cake layers. The cake balls make an excellent fun finger food appetizer before the main dessert.
Cultural Context
This cake brings together Irish festive spirit with a modern American twist. The top hat symbolizes the iconic image of St. Patrick’s Day festivities, and the rainbow layers connect to the popular Irish myth of leprechauns' pot of gold at the end of the rainbow. Using Lucky Charms marshmallows adds a playful cultural nod to Irish-themed treats most associate with the holiday in the US.
Pro Tips
- Make sure to thoroughly cool each cake layer before cutting or frosting to avoid tears and melting
- I learned the hard way never to skip the crumb coat it makes the final frosting look smooth and professional
- Use parchment paper as a guide when frosting the black hat band for clean, sharp edges
Common Recipe Questions
- → What pans are used to bake the layers?
An 8-inch pan is used for the base rim layer, while 6-inch pans bake the other layers that form the hat's top.
- → How are the rainbow colors achieved?
The batter is divided and dyed with red, orange, yellow, green, blue, and purple food coloring before baking each colored layer separately.
- → How is the marshmallow center created?
After layering and frosting, Lucky Charm marshmallows are poured into the hollowed centers of four layers, creating a surprising sweet core.
- → What frosting techniques are used for decoration?
Buttercream is dyed green for the crumb coat, then black and yellow tinted buttercream form a belt and buckle detail on the hat base.
- → Can leftovers be made from cake scraps?
Yes, cut-out centers are saved and combined with leftover frosting to form cake balls served alongside the finished cake.