- Nonstick cooking spray
- 3 cups cake flour, plus more for dusting
- 1 tablespoon baking powder
- 1 teaspoon kosher salt
- 3/4 cup hemp hearts (the hemp hearts can be toasted for a nuttier flavor)
- 12 tablespoons unsalted butter, softened
- 1 3/4 cups granulated sugar
- 4 large eggs, at room temperature
- 2 teaspoon pure vanilla extract
- 1 cup whole milk
- Red, yellow, green and blue food coloring (red + yellow for orange, blue + red for violet)
- 4 sticks unsalted butter, softened
- 10 cups confectioners’ sugar, sifted
- 1 tablespoon pure vanilla extract
- 1/4 teaspoon kosher salt
- 1/2 cup plus 2 tablespoons heavy cream
Tinted Hemp Hearts
- 1/4 cup hemp hearts
- 2 tablespoons powdered sugar
- food coloring gel
Bake the Cakes
- Preheat the oven to 350°. Coat three 8-inch round cake pans with nonstick cooking spray and line with parchment paper. Dust with cake flour, tapping out the excess.
- In a medium bowl, whisk the 3 cups of cake flour with the baking powder, salt and hemp hearts. In a stand mixer fitted with a paddle, cream the butter with the granulated sugar at medium speed, scraping down the bowl as needed, until light and fluffy, about 5 minutes. Add the eggs 1 at a time, beating well after each addition. Beat in the vanilla. Alternately beat in the dry ingredients and milk at low speed until just combined.
- Scoop the cake batter equally between each of 6 the medium bowls, about 1+ cup per bowl. Using a few drops of food coloring at a time, tint the batter in each bowl to create red, orange, yellow, green, blue, and violet layers. Scrape the batter from 3 of the bowls into the prepared pans and smooth the tops with a spatula. Bake the layers for 12 to 14 minutes, until a cake tester inserted into the centers comes out clean. Transfer the pans to a wire rack and cool for 10 minutes. Invert each layer onto a wire rack and remove the parchment.
- Clean the cake pans and repeat step 3 to bake the three remaining layers. After cooling, invert each layer onto a wire rack and remove the parchment.
Make the Vanilla Buttercream
- In a stand mixer fitted with the paddle, cream the butter at medium speed until light and fluffy, about 5 minutes.
- At low speed, add the confectioners’ sugar in 3 batches, beating well after each addition.
- Add the vanilla and salt. Beat at medium speed until smooth, about 6 minutes.
- Add the cream and beat until very light and fluffy, about 4 minutes.
Tinted Hemp Hearts
- Place the hemp hearts and powdered sugar in a zip-close plastic bag.
- Add a line of coloring gel about 2-inches long onto the hemp heart sugar mixture. Close the bag and massage the gel into the hemp hearts.
- Optional: Toast in a 350°F oven for 8 to 10 minutes, creating a nuttier flavor and crunch from the toasted sugar.
Assembling the Cake
- Set the violet cake layer on a cake plate.
- Using an offset spatula, spread the top with 1/2 cup of the vanilla buttercream. Repeat with the blue, green, yellow, orange and red layers.
- Spread or pipe 1 1/2 cups of the remaining buttercream over the top and sides of the cake in a decorative pattern.
- Top with tinted hemp hearts in a rainbow pattern.
- Refrigerate until the buttercream is firm, about 20 minutes.