Cake:

1. Preheat the oven to 350 F.
2. In a large bowl, use a mixer to cream butter until smooth and fluffy, about 1-2 minutes. Add sugar until beat until light and fluffy, another 1-2 minutes. Add the egg whites and continue to beat for another 2 minutes until combined. Add sour cream and vanilla extract and beat until combined. Slowly add the milk and mix until just combined.
3. Add flour, baking powder, baking soda, and salt. Beat on low speed until just combined. Do not overmix.
4. Pour the batter evenly into two 20-inch cake pans and place in the oven. Bake for 25 to 30 minutes until done. Check that a toothpick comes out clean and dry when inserted into the middle of the cake.
5. Allow the cakes cool down completely and cut them horizontally into half.

Frosting:

1. Mint Buttercream Frosting: Cream butter with a hand mixer until light and fluffy, about 1-2 minutes. Slowly add the icing sugar until fully incorporated. Beat in the peppermint extract. Gradually add in the cream and beat until smooth and creamy, about 3 minutes.
2. Cream Cheese Frosting: Using a hand mixer, beat the cream cheese and butter together until smooth and creamy. Add icing sugar and vanilla and beat until smooth and creamy, about 2 minutes.

Assembly:

1. Layer the cake with the buttercream frosting. If you have any buttercream frosting left, spread it evenly on the top and sides of the cake. Let the cake rest in the fridge for an hour.
2. Cover the cake with the cream cheese frosting and decorate with crushed and whole candy canes.