Preheat the oven to 350°F.

Spray an 8-inch square baking dish with nonstick cooking spray.

Place the butter and chocolate in a large microwave-safe mixing bowl. Microwave in 30 second increments, stirring between each, until the chocolate is fully melted. Allow to cool for 5 minutes.

Add the granulated sugar, brown sugar, vanilla, and eggs to the chocolate mixture. Stir vigorously until smooth.

Add the flour, cocoa, baking soda, and salt to the chocolate mixture. Stir vigorously with a rubber spatula until a thick batter forms and no lumps remain.

Fold the chocolate chips into the batter.

Pour the batter into the baking pan and level with a spatula.

Bake brownies on middle rack of oven until a toothpick inserted in the center comes out clean, about 25 minutes.

Check to see that brownies are done. Remove from oven or add time as needed.

Allow the brownies to cool at room temperature for 15 minutes. Refrigerate for 2 hours, then slice and serve.