This festive dessert will be the hit of your holiday party — and your social media feed. It relies on flavored gelatin inside and out — it’s used as a shortcut ingredient in the vibrant red glaze, and on the inside, you’ll find fun green streaks in the vanilla cake.
Special equipment: a chopstick, an immersion blender and an instant-read digital thermometer
Prepare the cake layers in two 8-inch cake pans according to the package directions; let cool completely in the pans on a rack. Level the domed tops of the cakes with a serrated knife, then invert the cakes out of their pans. Clean and dry the cake pans; return the cooled cakes cut-side up to the pans. Poke the cakes every 1/2 inch with a chopstick.
Stir together the lime gelatin and 1 cup boiling water in a small bowl until completely dissolved; let cool for 10 minutes. Pour over the cakes and refrigerate until the gelatin is absorbed, about 30 minutes.
Remove the cakes from the pans (if they stick, dip the pans in hot water for 10 seconds to loosen). Place one cake on a large plate. Frost the top with 1 cup of the frosting in an even layer. Top with the second cake and frost the whole cake with the remaining frosting, making it as smooth as possible. Freeze for 1 hour.
Meanwhile, stir together the raspberry gelatin and 1/4 cup boiling water in a small bowl until completely dissolved.
Combine the sugar, corn syrup and 1/4 cup water in a medium saucepan. Bring to a boil and cook until the sugar is dissolved and the mixture is clear, about 2 minutes. Remove from the heat and stir in the raspberry gelatin mixture and the white chocolate. Let sit until the chocolate has melted, about 2 minutes. Stir in the condensed milk and blend with an immersion blender until completely smooth. Let the mixture cool to 95ºF on an instant-read digital thermometer.
Remove the cake from the freezer and place on a cooling rack set over a rimmed baking sheet. Pour about two-thirds of the raspberry-white chocolate glaze over the cake. Swirl several drops of red food coloring into the remaining glaze and then pour it over the cake (the whole cake should be covered in the glaze). Let set for 15 minutes, then transfer the cake to a serving platter and refrigerate until firm, 1 to 2 hours.