Preheat your oven to 350°F (175°C). Lightly grease an 8x8-inch baking pan or line it with parchment paper.
In a medium mixing bowl, whisk together the melted butter and sugar until smooth.
Add the eggs and mix until fully incorporated.
Stir in the cocoa powder and flour until a thick brownie batter forms.
Pour the batter into the prepared pan and spread evenly.
Bake for 22-25 minutes, or until the center is set. Cool completely before slicing.