Step 1

Preheat oven to 350 degrees F. Grease three 8-inch round pans with baking spray and line with parchment rounds.

Step 2

Sift together cake flour, baking powder, baking soda and salt into a large bowl.

Step 3

In another large bowl, cream the butter, sugar and orange zest together with an electric mixer until light and fluffy, about 3 - 5 minutes on medium speed.

Step 4

Beat in the vanilla bean paste and oil until combined. Beat in the eggs, one at a time, until each is combined.

Step 5

Mix in half of the dry ingredients on low speed for 1 minute. Stop the mixer and add the orange juice and champagne. Mix until combined. Add the rest of the dry ingredients and beat until combined.

Step 6

Divide evenly among the prepared cake pans. Bake for 20-25 minutes or until a toothpick inserted in the center comes out almost clean.

Step 7

Let cakes cool in pans for at least 10 minutes before turning onto wire racks to cool completely. Meanwhile, you could start on the frosting.

Step 8

Whisk together sugar and egg whites in a heatproof mixing bowl set over (not in) a pan of simmering water. Whisk until warm and sugar is dissolved (mixture should feel completely smooth when rubbed between your fingers), 2 to 3 minutes. Remove from heat.

Step 9

With an electric mixer on medium speed, whisk egg white mixture 5 minutes (using the whisk attachment). Increase speed to medium-high, and whisk until stiff, glossy peaks form and meringue has cooled (test by feeling bottom of the bowl), about 6 minutes.

Step 10

Reduce speed to medium and switch to the paddle attachment. Add butter, one piece at a time, beating well after each addition. Keep beating until the buttercream comes together (IT WILL). Beat in orange zest and orange juice until smooth and silky.

Step 11

Use immediately or store in an airtight container in the fridge for up to a week.

Step 12

Place one layer of cake on a cake stand or serving platter. Spread about ½ cup of frosting over the top using an offset spatula. Top with another layer of cake and repeat with another layer of frosting. Smooth with an offset spatula. Top with final layer of cake. Frost cake with a crumb coat of buttercream and refrigerate for at least 30 minutes. Finish frosting cake and decorate as desired.