Preheat oven to 350 degrees F (175 degrees C). Grease and flour a 9x13-inch baking pan.
Combine sugar, flour, cocoa powder, baking soda, baking powder, and salt in a large bowl.
Mix buttermilk, oil, coffee, eggs, and vanilla extract together in a bowl. Pour over sugar mixture in the large bowl; beat with an electric mixer on medium speed until batter is smooth and thin, about 2 minutes. Pour batter into the prepared baking pan.
Bake in the preheated oven until a toothpick inserted into the center comes out clean, about 35 minutes.