Buttermilk and chocolate squares are the secret ingredients .
5 ounces semi sweet chocolate, coarsely chopped
2 1/4 cups cake flour (not self-rising)
3/4 cup unsweetened cocoa (preferably Dutch processed)
1 1/2 teaspoons baking powder
1/2 teaspoon baking soda
1/2 teaspoon salt
1 cup lukewarm coffee (or water, if you don’t like the taste of coffee)
1 cup buttermilk
1 1/4 cups unsalted butter, room temperature
2 cups granulated white sugar
5 large eggs, room temperature
1 1/2 teaspoons pure vanilla extract
Preheat oven to 350 degrees F (180 degrees C) and place oven racks in the upper and lower third of the oven. Lightly butter and flour a 9×13 pan. In a heatproof bowl, placed over a saucepan of simmering water, melt the chopped chocolate. Remove from heat and let cool to room temperature.
In a separate bowl, sift the flour, cocoa powder, baking powder, baking soda and salt.
In a small bowl, combine the coffee (or water) and buttermilk.
In the bowl of your electric mixer, or with a hand mixer, beat the butter until smooth and creamy. Add the sugar and continue beating until the mixture is fluffy (about three to five minutes). Scrape down the sides of the bowl as needed. Add the eggs, one at a time, mixing well after each addition. Add the vanilla extract and beat to combine. Then add the melted chocolate and beat until incorporated. Add the coffee/ buttermilk mixture and flour mixture in three additions, beginning and ending with the flour mixture. Beat only until the ingredients are mixed together.
Divide the batter evenly among the three prepared pans and smooth the tops, then rap pan on counter several times to eliminate air bubbles. Bake for about 30 – 35 minutes or until a toothpick inserted in the center comes out clean and the tops spring back when lightly pressed. (I like to rotate the pans about halfway through baking to ensure even baking.) Remove from oven and place on a wire rack to cool for about 15 minutes.