Preheat your oven to 175°C (350°F). Line the baking pan with parchment paper or grease well with non-stick spray.

Melt the butter in a heatproof bowl using a microwave or a small saucepan. Allow to cool slightly.

Whisk together the melted butter, granulated sugar, and brown sugar until smooth and glossy.

Add eggs one at a time, whisking well after each addition. Stir in the vanilla extract.

In a separate bowl, sift together the flour, cocoa powder, and salt.

Gently fold the dry ingredients into the wet mixture, mixing just until combined. Avoid over-mixing.

If using, fold in the chocolate chips.

Pour the batter into the prepared baking pan, spreading evenly with a spatula.

Bake for 23-25 minutes, until the center is just set and a toothpick inserted comes out with a few moist crumbs. Do not overbake for fudgier brownies.

Cool completely in the pan before lifting out with parchment and slicing into 12 even squares.