You can make a box brownie mix according to package directions, or make my favorite brownie recipe as directed in step 2. Let them cool completely. It’s probably easiest to make these straight in the pan without foil, or use parchment instead for ease of cutting.
To make my brownie recipe: Preheat oven to 350°F. Line a 9x13” pan with foil or parchment and spray with nonstick cooking spray. 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 20-25 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.
Melt chocolate in a large microwave safe bowl for 30 seconds, then stir, heat for 30 seconds again, then stir well, then heat on 10 second increments, stirring between each, until smooth. Let cool 5 minutes.
Beat cream cheese in a large bowl with a hand mixer until smooth. Add chocolate and mix until combined, then mix in vanilla. Fold in half of the Cool Whip (one 8 ounce container).
Spread the chocolate mixture on top of the brownies, then top with second container of Cool Whip. Use a potato peeler to shave some additional baking chocolate all over the top.
Chill for at least one hour before serving to allow it to set. Store in the refrigerator for up to 3 days.