Pre-heat oven to 375F with a rack placed in the middle of the oven.
Whisk flour, cocoa powder, baking soda, salt, and sugar together in a large bowl.
With a fork, stir in vanilla, vinegar, oil, and hot water or brewed coffee until completely mixed.
Pour batter into a lightly greased 8" square cake pan, or cupcake papers in a muffin pan.
Bake for 35-40 minutes for the cake. Bake 20-25 minutes for the cupcakes.