Preheat the oven to 350 degrees. Spray an 8 x 8 baking dish with cooking spray. You can line it with parchment paper as well if desired.

In a small saucepan heat the butter, bittersweet chocolate, and semi-sweet chocolate over medium heat. Stir constantly until the chocolate and butter are melted and well combined.

Remove from heat.

In a large bowl combine the sugar, brown sugar, eggs, and egg yolks. Whisk in the salt and vanilla.

Pour the chocolate butter mixture into the sugar mixture and whisk until just combined.

Slowly stir in the flour and mix until everything is combined. Fold in the chocolate chips.

Pour the batter into the prepared bowl and bake for 40-45 minutes. The middle will be gooey when you pull them out of the oven!

Remove from oven and cool for at least 45 minutes.

Cut into squares and serve with ice cream.