Step 1

Preheat oven to 350°F. Prepare red velvet cake mix according to package directions. Divide batter evenly among 3 (9-inch) round cake pans coated with baking spray.

Step 2

Bake in preheated oven until a wooden pick inserted in centers of cakes comes out clean, about 25 minutes. Cool in pans 10 minutes. Invert cakes onto wire racks; cool completely, about 45 minutes.

Step 3

Beat softened butter and cream cheese with a stand mixer fitted with a paddle attachment on medium speed until smooth, about 2 minutes. With mixer on low speed, gradually add powdered sugar, white chocolate, and vanilla. Increase speed to medium-high; beat until fluffy, about 2 minutes. (You will have about 10 cups frosting.)

Step 4

Place a cake plate on a lazy Susan or stand. Put 1 cake layer on plate; spread top with 1¼ cups frosting. Repeat with remaining 2 cake layers and 2½ cups of the frosting. Using a large offset spatula, spread a thin layer of frosting (about 1 cup) over sides of entire cake. Using an offset spatula or the back of a teaspoon, gently press into outer edge of frosting on top cake layer. Spin cake to create a spiral pattern in frosting, moving to center of cake. Remove cake plate with cake from lazy Susan, and chill until frosting is firm and set, about 30 minutes.

Step 5

Place remaining frosting (about 5¼ cups) in a piping bag fitted with a Wilton 104 petal tip; set aside.

Step 6

Return cake plate with cake to lazy Susan. Hold piping bag with pointed (thin) end of the tip facing straight up. Starting at the top of 1 side of the cake, turn it while piping a ring around it, gently moving the piping bag up and down slightly to create a ruffled effect. Pipe another ruffled ring a bit lower on cake, overlapping first ring slightly. Repeat process around cake, making each ring a little lower and overlapping slightly, until you reach the bottom.