Preheat your oven to 350 degrees
Grease a 10" oven safe skillet or deep round baking dish and set aside for now
In a large bowl, melt 3/4 cup of butter and 6 ounces of chopped chocolate using a double boiler or with 15 second increments in the microwave until soft enough to whisk smooth and set aside to cool for 5 minutes
Once the chocolate mixture has cooled slightly, add 3 large eggs and 2 teaspoons of vanilla extract and whisk until fully incorporated
Add 1/2 cup of granulated sugar and 1/2 cup of packed brown sugar and whisk to combine
Sift 2/3 cup of all purpose flour with 3 tablespoons of natural unsweetened cocoa powder, 1 teaspoon of espresso powder and 1/2 teaspoon of salt into the chocolate mixture and mix until just combined
Transfer the batter into the greased skillet
Drop tablespoons of softened creamy peanut butter over the batter and use a butter knife or chopstick to swirl the peanut butter into the batter (see photos above)
Bake in a 350 degree oven for 28-30 minutes or until a toothpick will come out of the center with only a few moist crumbs (be careful to avoid over-baking the brownie)
Transfer the skillet onto a heat proof surface and let it sit for 5-10 minutes before serving with vanilla ice cream