Brownies

Preheat the oven to a moderate baking temperature and line a small baking pan with parchment paper.

Gently melt the butter until just liquid, then let it cool slightly so it is warm but not hot.

Whisk the sugar into the warm butter until the mixture looks thick and glossy.

Beat in the eggs one at a time, then mix in the vanilla extract until the batter looks smooth and slightly thickened.

Sift the flour, cocoa powder, and salt together, then fold them into the wet mixture just until no dry spots remain.

Fold in the chopped dark chocolate if using, spreading the batter evenly into the prepared pan.

Bake until the top is set and a tester comes out with a few moist crumbs, then let the brownies cool in the pan before slicing.