Begin preheating your waffle iron according to the manufacturer's instructions.
In a large mixing bowl, whisk together the all-purpose flour, white sugar, unsweetened cocoa powder, baking powder, and salt.
In another bowl, beat the milk, eggs, vegetable oil or melted butter, and vanilla extract until everything is well combined.
Pour the wet ingredients into the dry ingredients and stir until just mixed. It's okay if there are a few lumps; you really don't want to overmix the batter. If you want to add chocolate chips, add them at the same time as the wet ingredients or drop them in once they're added ot your waffle maker.
Grease the waffle iron with a little bit of oil or non-stick spray if it isn't non-stick, then ladle the batter onto the waffle iron and cook according to the iron's instructions, usually for about 3-5 minutes, until the waffles are golden brown and crisp.
Carefully remove the waffles and serve immediately with your favorite toppings like whipped cream, fresh berries, or a drizzle of chocolate sauce. Recipe makes 8 to 10 waffles.