There are a multitude of chocolate cake recipes both in print and in the blogsphere. Between a friend and myself, we tested at least a half-dozen recipes. Some included as many as six eggs in the batter while others had as few as one egg.
There were recipes that included melted chocolate, as well as cocoa powder, others only included cocoa powder. Through testing we discovered that melted chocolate creates a drier cake than I desired. If I had read BakeWise  before that trial and I would have discovered the results of melted chocolate. It was so dry, I opted to leave it out for the sake of the cake.
We also came to the conclusion that even though butter is taster, a canola or vegetable oil works better in a chocolate cake as it also counters the drying effect of the cocoa powder. Buttermilk gives it a slight tang, but whole milk works fine too. I wouldn’t even think of using skim, 1 or 2 percent milk. I hope you won’t either. After many attempts this one is a winner.
3/4 cup (2 1/2 oz/70 g) non-alkalized cocoa powder, plus extra to dust sides of pans
2 teaspoons baking powder
1 1/2 teaspoons baking soda
2 cups (14 oz/400 g) granulated sugar
2 cups (9 oz/255 g) unbleached all-purpose flour
1 teaspoon kosher salt
1 tablespoon espresso powder
1 cup (8 oz) buttermilk
1/2 cup (4 oz) vegetable oil
2 teaspoon pure vanilla extract
2 large eggs
1 cup (8 oz) boiling water
Set a rack in the middle of the oven and preheat to 350°F. Butter two 9-inch cake pans with 2-inch sides. Line the bottom of the pans with parchment paper and dust the sides with cocoa powder, tapping out excess. Set aside.
In the bowl of a stand mixer using the paddle attachment mix together the cocoa powder, baking powder and baking soda, sugar, flour, salt, and espresso powder. (If any of the ingredients have lumps, i.e., the cocoa powder, sieve first and then add to the bowl.)
In a 2 cup glass measuring cup add the buttermilk, vegetable oil, and vanilla extract. Using a fork, beat the eggs into the buttermilk mixture.
Add the buttermilk mixture to the flour mixture and beat on medium speed for 2 minutes. Pour in boiling water and beat for an additional minute. (The batter will be thin.) Be sure check that the batter at the bottom of the bowl is fully incorporated.
Divide the batter evenly between the two prepared pans. Bake until toothpick inserted into centers comes out clean, about 30-35 minutes. Cool cakes in pans on racks about 10 minutes. Turn out onto racks and cool completely prior to frosting  the cake.