Preheat oven to 350 F and line a 9x9 baking pan with parchment paper. Allow parchment to hang over the side to use as handles later.
Pour melted butter over chocolate chips in a bowl and allow to sit for a minute to soften chocolate. Stir with rubber spatula.
3/4 cup unsalted butter, 2/3 cup semi-sweet chocolate chips
Add eggs, cocoa, sugar and vanilla and stir.
3 large eggs, 1/2 cup unsweetened cocoa powder, 1 1/2 cups granulated sugar, 1 teaspoon vanilla extract
Stir in the flour just until no more traces of flour remain.
4.2 ounces all purpose flour
Scrape the batter into the prepared pan. Bake for 30 minutes, or until a toothpick inserted in the center comes out clean.
Allow brownies to cool in pan for at least five minutes. Use the parchment handles to lift the brownies out and onto a cooling rack. Allow to cool completely before cutting.