In a small saucepan, combine granulated sugar, cornstarch, and salt, then stir in orange juice over medium heat. Cook for about 1 minute until thickened.

Preheat your oven to 350°F (175°C). Line three 6-inch round cake pans with parchment paper and grease the sides.

In a large bowl, cream together unsalted butter and granulated sugar until light and fluffy, about 3-5 minutes. Add egg whites one at a time, mixing well after each addition. Alternate adding cake flour and milk, mixing until smooth.

Divide the batter evenly among the prepared pans and bake for 30-35 minutes, or until a toothpick comes out clean. Allow to cool in pans for about 10 minutes before transferring to wire racks.

Melt the white baking chocolate with the heavy whipping cream and set aside to cool. Combine egg whites, granulated sugar, cream of tartar, and salt in a bowl over simmering water until reaching 160°F. Beat until stiff peaks form, then mix in cooled chocolate and butter.

Once cakes are cool, layer one on a serving plate, spread orange curd, add the second layer, and repeat. Coat the outside of the cake with remaining buttercream and sprinkle coarse sugar on top.

Create bunny decorations using melted candy melts and attach sugar beads or chocolate drizzle. Arrange on top of the cake.