Let’s build this magnificent St. Patrick’s Day Cake!

Cake:

Step 1: Preheat and Prepare Pans

Preheat your oven to 350°F (175°C). Line one 8-inch cake pan and five 6-inch cake pans with parchment paper rounds. Coat the pans with cooking spray.

Step 2: Combine Dry Ingredients

In a large bowl, whisk together the flour, baking powder, and salt.

Step 3: Cream Butter and Sugar

In another large bowl, using a handheld mixer on medium-high speed (or a stand mixer fitted with the paddle attachment), beat the granulated sugar and softened butter until combined.

Add the oil and beat until the mixture is smooth and creamy.

Step 4: Add Eggs and Vanilla

Add the eggs one at a time, beating well after each addition. Then, beat in the vanilla extract.

Step 5: Alternate Adding Dry Ingredients and Liquids

Add about one-third of the dry ingredients to the wet ingredients and beat on medium-low speed until just a few dry streaks remain.

Add the milk and beat until incorporated.

Add another one-third of the dry ingredients and beat on medium-low speed until just a few dry streaks remain.

Add the sour cream and beat until incorporated.

Add the remaining dry ingredients and beat until just combined. Be careful not to overmix.

Step 6: Divide and Color Batter

Divide the batter evenly among six bowls.

Dye one bowl of batter red, one orange, one yellow, one green, one blue, and one purple, using gel food coloring for the most vibrant colors.

Step 7: Bake the Cakes

Pour the purple batter into the prepared 8-inch cake pan. Bake for 15 to 18 minutes, or until a tester inserted into the center comes out clean. Let cool completely.

Pour the remaining batters (red, orange, yellow, green, blue) into the prepared 6-inch cake pans. Bake for 30 to 35 minutes, or until a tester inserted into the center comes out clean. Let cool completely.

Step 8: Make Ahead (Optional)

Cake layers can be baked 1 day ahead. Wrap them tightly in plastic wrap and refrigerate, or freeze for up to 2 weeks.

Frosting & Assembly:

Step 1: Make the Frosting

In a large bowl, using a handheld mixer on medium speed (or a stand mixer fitted with the paddle attachment), beat the powdered sugar and softened butter until smooth.

Add the heavy cream, vanilla extract, and salt and beat until combined and fluffy.

Step 2: Trim and Cut Cake Layers

Trim the tops of the cooled cake layers as needed to make them level.

Using a 3-inch round cookie cutter, cut out the center of the orange, yellow, green, and blue cake layers. Reserve the cut-out centers for another use (cake pops, perhaps!).

Step 3: Assemble the Cake

Place the purple layer on a cake stand or platter. Frost the top with a thin layer of buttercream.

Top with the blue cake layer. Frost with more buttercream and repeat with the green, yellow, and orange cake layers in that order, frosting the top of the orange layer with buttercream.

Pour the Lucky Charms marshmallows into the center of the cake, filling the hole created by the cookie cutter.

Top with the red cake layer.

Step 4: Crumb Coat

Frost the top and outside of the cake with a thin layer of buttercream to create a crumb coat. This will seal in any loose crumbs and create a smooth surface for the final frosting.

Refrigerate the cake until the crumb coat is well chilled, at least 30 minutes or up to 2 hours.

Step 5: Final Frosting and Decoration

Scoop out about 1 1/2 cups of the buttercream and set aside.

Dye the remaining buttercream green using gel food coloring.

Using an offset spatula, frost the cake with the green buttercream, smoothing the sides with a bench scraper.

Step 6: Create the Hat Details

Divide the reserved buttercream into two portions: about 1 cup and 1/2 cup.

Dye the 1 cup portion black and the 1/2 cup portion yellow.

Using an offset spatula, frost a 1-inch-thick belt with the black frosting at the base of the cake, just above where the “rim” of the hat would be. To help create a smooth line, you can wrap the cake in parchment paper above where you’ll frost, covering the “rim” of the hat with parchment as well.

Transfer the yellow buttercream to a piping bag fitted with a medium round tip. Pipe a buckle over the black belt.