Preheat the oven to 350°F. Cut two 9-inch circles of parchment to line the bottoms of two 9-inch nonstick cake pans (trace the pans for ease). Lay the parchment in the pans. Lightly mist the papers and the sides of the pans with spray.

In a medium mixing bowl, sift together the flour, cocoa powder, baking powder, baking soda, espresso, and salt.

In a large mixing bowl, using a sturdy whisk (an electric mixer can be used, but be careful not to over mix), mix the buttermilk, vinegar, and vanilla until well combined. Whisk in the egg whites, the sugar, and the yogurt and continue mixing until blended. Gradually stir in the dry ingredients until just smooth. Divide the batter evenly among the pans. Bake the cakes about 16 to 18 minutes, or until a toothpick in the center comes out dry (a few crumbs are okay).

Cool the cakes side by side on a wire cooling rack in the pans for 10 minutes. Then carefully flip the cakes onto the rack. If the cakes stick to the sides of the pans, gently run a butter knife around the rims of the pans to loosen them.

Meanwhile, prepare the Chocolate Buttercream Frosting.

When the cakes are completely cool, place one cake, flat side down, on a serving platter. Spread 3/4 cup of the frosting over the top of the cake. Top it with the second cake, flat side down. Spread the remaining frosting evenly over the top and sides of the cake. Slice the cake into 14 equal wedges. Serve immediately or store in an airtight plastic container for up to 3 days in the refrigerator.

Add the butter, cream cheese, vanilla, and salt to a large mixing bowl. Using an electric mixer fitted with beaters, beat them on high speed until smooth.

Add half of the powdered sugar. Beat on low speed until well combined. Beat in the remaining powdered sugar then the cocoa powder until combined.

Add the milk and then beat on high speed until fluffy. Tightly wrap the frosting with plastic wrap until the cakes are cooled (do not refrigerate it before icing the cake). Makes 2 1/4 cups.