St. Patrick's Day Cake

1 . Stage

Preheat oven to 350°. Line 1 (8") cake pan and 5 (6") cake pans with parchment; coat pans with cooking spray. In a large bowl, whisk flour, baking powder, and salt. 

2 . Stage

In another large bowl, using a handheld mixer on medium-high speed, beat granulated sugar and butter until combined. Add oil and beat until smooth and creamy. Add eggs, one at a time, beating well after each addition, then beat in vanilla. 

3 . Stage

Add about one-third of dry ingredients and beat on medium-low speed until just a few dry streaks remain. Add milk and beat until incorporated. Add another one-third of dry ingredients and beat on medium-low speed until just a few dry streaks remain. Add sour cream and beat until incorporated. Add remaining dry ingredients and beat until just combined. 

4 . Stage

Divide batter among 6 bowls. Dye one bowl of batter red, one orange, one yellow, one green, one blue, and one purple. 

5 . Stage

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

6 . Stage

Pour remaining batters into prepared 6" cake pans. Bake cakes until a tester inserted into the center comes out clean, 30 to 35 minutes. Let cool. 

7 . Stage

Make Ahead: Cake layers can be baked 1 day ahead. Wrap in plastic and refrigerate, or freeze up to 2 weeks.

8 . Stage

In a large bowl, using handheld mixer on medium speed, beat powdered sugar and butter until smooth. Add cream, vanilla, and salt and beat until combined.

9 . Stage

Trim tops of cooled cakes as needed. Using a 3" round cookie cutter, cut out center of orange, yellow, green, and blue cake layers.

10 . Stage

Place purple layer on a cake stand or platter. Frost top with a thin layer of buttercream. Top with blue cake layer. Frost with more buttercream and repeat with green, yellow, and orange cake layers in that order, frosting top of orange layer with buttercream. Pour marshmallows into center of cake. Top with red cake layer. Frost top and outside of cake with a thin layer of buttercream to create a crumb coat. Refrigerate until well chilled, at least 30 minutes or up to 2 hours.

11 . Stage

Scoop out about 1 1/2 cups buttercream. Dye remaining buttercream green. Using an offset spatula, frost cake with green buttercream, smoothing with a bench scraper.

12 . Stage

Divide reserved buttercream into about 1 cup and 1/2 cup. Dye 1 cup black and 1/2 cup yellow.

13 . Stage

Using offset spatula, frost a 1"-thick belt with black frosting at base of hat above the rim. To help create a smooth line, wrap cake in parchment above where you’ll frost, covering rim of hat with parchment as well.

14 . Stage

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