For Cake:

1. Preheat oven to 350º F. 
2. Generously grease and flour two 9-inch round cake pans. 
3. In a medium bowl, mix together flour, cocoa and baking powder and set aside. 
4. In a large bowl (or bowl of a stand mixer), cream the butter and sugar. Add the eggs and yolk one at a time. Beat in emulsion and salt, then the water. 
5. Add flour mixture alternating with the buttermilk. Dissolve the baking soda into the vinegar and blend into the batter. 
6. Pour evenly into cake pans and bake for 25 to 30 minutes until toothpick inserted into center comes out clean. Cool cakes and remove from pan. 

For Cream Cheese Frosting:

1. Using an electric mixer, or stand mixer with whisk attachment, cream butter and sugar on low speed until combined, then beat on medium speed for 3 to 4 minutes. 
2. Add cream one tablespoon at a time, until desired consistency is achieved. 
3. Add emulsion and salt and beat an additional 1 minute. 

Recipe Tips:

1. For 2 individual 9-inch cakes, spread icing on top of cakes, then on sides. Decoratively pipe an icing a border around top and base, if desired.
2. For a 2-layer cake - spread icing on top of one cake layer then place second on top and ice top and sides.
3. For a 4-layer cake, cut each 9-inch cake horizontally to make 4 layers.