Preheat the oven to 350°F (175°C). Grease a 9-inch pie dish or cake pan that is 2–3 inches deep.
In a mixing bowl, combine the milk and lemon juice or vinegar. Let it sit for a few minutes.
Add the sugar, cocoa powder, vanilla extract, and instant coffee or espresso powder. Whisk until combined.
Add the flour, baking soda, baking powder, and salt. Mix, then add the melted butter and stir until you have a smooth batter. Avoid overmixing.
Spread the chocolate batter evenly into the prepared baking dish. Sprinkle one tablespoon of sugar evenly over the batter, (this is optional) it will form a crust after baking.