Grandma Jean's Buttermilk-Chocolate Cake

Preheat the 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 mixing bowl; whisk until fully combined. Add coffee, buttermilk, oil, eggs, and vanilla extract. Beat with an electric mixer on medium speed for 2 minutes; batter will be thin. Pour into the prepared baking pan.

Bake in the preheated oven until a toothpick inserted into the center comes out clean, 35 to 40 minutes. Let cool completely.