Preheat the oven to 350°F (175°C).

In a microwave-safe bowl, melt the butter.

In a large mixing bowl, combine the melted butter and granulated sugar. Mix well.

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

In a separate bowl, whisk together the flour, cocoa powder, and salt. Gradually add the dry ingredients to the wet ingredients, mixing until just combined.

Fold in the chocolate chips and chopped walnuts, if using.

Pour the batter into a greased 9x9-inch baking dish and spread evenly.

Bake for 25 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs.

Allow the brownies to cool before cutting into squares.

Serve and enjoy!