Use a wooden spoon or spatula to stir until fully combined, mixing until no streaks of flour remain, but avoiding over-mixing. The batter will be thick.
Press into the prepared baking tin as evenly as possible. Bake for 18-22 minutes, or until the edges are set but the middle is still slightly soft.
Cool for at least ten minutes before carefully removing from the tin and cooling fully on a wire rack. Leftover brownies will keep in an airtight container for up to a week and freeze well.
Notes
If you don’t have a 20×20 cm tin, a 15×20 cm tin or another that is slightly larger or smaller will work fine. The baking time will change slightly so keep an eye on your brownies.This is a thick batter and must be pressed into the tin. It’s normal, you haven’t made a mistake.Use 70% or higher chocolate. Sweeter chocolate results in a less desirable texture, and makes the brownies far too sweet.