Preheat oven to 350°F. Line a 9x9” pan with foil or parchment and spray with nonstick cooking spray (be sure to use original and NOT the kind with flour!) (You can also bake these in a 9x13" pan for more but thinner brownies, but baking time will be affected.)
Place baking chocolates and butter in a large microwave safe bowl. Heat in 30 second increments, stirring between each, until melted and smooth (about 2 minutes depending on your microwave).
Stir sugar into chocolate mixture, then stir in eggs until well mixed. Add the vanilla, cocoa, and salt and stir until smooth, then carefully stir in the flour.
Pour batter into the pan and bake for about 22-25 minutes until a toothpick comes out with just a few crumbs an inch from the side of the pan. I like to make these a little underdone so they stay fudgy and rich.
Cool completely in the pan then cut into squares and serve. Store in an airtight container for up to 4 days or freeze for up to one month.
Tip: add any gluten-free candy or chopped cookies in step 3 after adding the flour for a fun twist.