Chocolate Triple Berry Layer Cake

shortening and flour for greasing the pans 
1 package devil's food cake mix 
3 T unsweetened cocoa powder 
1 ½ c buttermilk 
1/3 c oil 
3 eggs 
1 t vanilla extract 
1 recipe Chocolate Buttermilk Frosting (below) 
½ jar Emily G's Triple Berry Jam 

Preheat oven to 350°. Grease and dust with flour 2 9-inch round cake pans. In a large bowl, add cake mix, cocoa, buttermilk, oil, eggs, and vanilla. Blend for 2-3 minutes on medium speed with an electric mixer. Scrape sides as needed. Pour into prepared pans and smooth batter with a spatula. Bake 28 minutes or until a toothpick stuck in the middle comes out clean. 
Allow the cakes to cool in the pan for 20 minutes. Run a knife along the sides of the pan and carefully flip the cake out. Once the cakes are room temperature, carefully cut the rounded top off the cakes so that they are flat. Spread the Triple Berry Jam on top of one cake. Take the second cake and place it on top of the first, crumb side down (so that the bottom of the cake is now the top). Ice the cake, starting with the sides and finishing with the top.  
CHOCOLATE BUTTERMILK FROSTING

1 stick of butter, room temp 
¾ c unsweetened cocoa powder 
3 c confectioner sugar 
¼ c buttermilk 
2 T milk 
2 t vanilla extract 
pinch salt 

Blend all ingredients with a mixer on low until light, fluffy, and completely combined.