Preheat the oven to 350 degrees Fahrenheit and line a 9 by 13 inch baking pan with parchment paper.

In a medium saucepan, melt 1 cup unsalted butter over low heat. Add 8 oz semisweet chocolate and stir until melted and smooth. Remove from heat and let cool for a few minutes.

Whisk in 1 and 1/4 cups granulated sugar and 3/4 cup light brown sugar into the warm chocolate mixture until combined.

Beat in 4 large eggs one at a time, mixing well after each addition. Stir in 2 teaspoons vanilla extract.

In a separate bowl, sift together 3/4 cup all purpose flour, 1/2 cup unsweetened cocoa powder, and 1/2 teaspoon salt.

Gradually fold the dry ingredients into the wet chocolate mixture, mixing just until combined to avoid overmixing.

Pour the batter into the prepared pan and smooth the top with a spatula.

Bake in the preheated oven for 30 to 35 minutes or until a toothpick inserted in the center comes out with a few moist crumbs.

Allow the brownies to cool in the pan for at least 30 minutes before slicing and serving.