Preheat the oven to 350?F (175?C). Grease and line a 9x9 inch baking pan with parchment paper.

In a mixing bowl, whisk together the melted butter and sugar until well combined.

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

Sift together the flour, cocoa powder, and salt in a separate bowl. Gradually fold the dry ingredients into the wet ingredients until just combined.

Fold in the chocolate chips if using.

Pour the brownie batter into the prepared baking pan and spread evenly.

Bake in the preheated oven for 20-25 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs.

Remove from the oven and let cool in the pan for about 10 minutes before transferring to a wire rack to cool completely.