Preheat the oven to 325 degrees. Prep a 9×13 cake pan with cake goop, baking spray, or shortening + flour. Set aside.

In a large bowl, hand-whisk together buttermilk, sour cream, eggs, vegetable oil, and vanilla. Sift in the cake mix, then gently stir to combine.

Spread the batter into the prepared baking pan and bake for 22-25 minutes. Let cool completely.

Once cooled, flip the cake onto the counter on a sheet of parchment paper and slice the cake in half using a cake leveler.

Add the bottom layer back into the 9×13 pan. Spread on the whipped cream filling, then flip the other cake layer onto the filling.

Chill a metal bowl and whisk in the freezer for 5 minutes. In a stand mixer, whip the heavy cream until stiff peaks form, then mix in vanilla, almond extract (if using), and powdered sugar.

Spread the whipped cream filling on the bottom cake layer, then add the top layer.

In a small bowl, heat heavy cream and white chocolate until smooth. Set aside.

In a stand mixer, whip the butter until light and fluffy. Add salt and vanilla, mix in the white chocolate mixture, and then add powdered sugar. Add more heavy cream if needed.

Frost the cake, reserving about 2 1/2 – 3 cups of buttercream for the border.

Add red gel coloring to the reserved buttercream and pipe a red wavy pattern around the cake.

Pipe a shell border around the outside of the cake, sprinkle green sanding sugar in the middle, and add festive sprinkles around the edge.