Preheat oven to 350 degrees. Line a 9x13 inch pan with foil and spray with non-stick cooking spray.

In a large saucepan, over medium heat, melt butter and both chocolates together. Keep stirring until they are completely melted and mixed together. Remove from heat and add in both sugars. Stir until combined. Allow mixture to cool slightly. Your mixture should be warm, but not hot (you don’t want the eggs to scramble when you add them in). Add in 1 egg at a time and really whisk the mixture. You want each egg fully incorporated and glossy before adding in the next egg. Repeat until all the eggs are mixed in.

Add in your salt, vanilla, and flour. Mix together until the flour is just barely incorporated. Do not overmix.

Pour batter into your prepared baking dish. Bake for 30-40 minutes until a toothpick inserted in the center comes out clean. Cool and cut into squares. Serves 15.