Instructions

1. Place a rack in the upper third of the oven and preheat to 325 degrees F. Grease an 8×8-inch baking pan. Line with parchment paper so that it overhangs on two sides and grease the parchment paper as well.
2. Boil two inches of water in a medium saucepan. Combine butter, unsweetened chocolate, semi-sweet chocolate in a heat proof bowl and place over the simmering water. Stir until chocolate and butter are melted. Use a pot holder to remove the bowl from the double boiler. Whisk in the sugar and vanilla extract.
3. Allow the chocolate mixture to cool slightly then whisk in the eggs, one at a time whisking very well between each addition.
4. In a small bowl, whisk together flour, baking powder and salt.
5. Fold in the flour mixture into the chocolate mixture until thoroughly combined and spoon into prepared pan.
6. To make the Peanut Butter Filling: whisk together melted butter, powdered sugar, peanut butter, salt and vanilla extract until smooth.
7. Spoon the peanut butter mixture over the top of the brownie batter and use a butter knife to swirl it into the batter. Bake for about 40 minutes until a skewer inserted in the center comes our mostly clean with just a few moist crumbs.
8. While they’re baking, make the frosting: In the bowl of an electric mixer fitted with the paddle attachment, beat the butter on medium speed until soft, about 1 minute, then add in the maple syrup and keep mixing for about 1 minute more. Add 1 1/2 cups of the confectioners’ sugar, salt, and vanilla. Beat on low speed until the sugar is well incorporated. Add another 1/2-1 cup sugar. Add more sugar as needed to thicken the frosting. Beat on medium speed until the frosting is smooth and fluffy, about 4 minutes.
9. Let the brownies cool for at least 30 minutes before frosting with the maple frosting. Store at room temperature. These brownies also freeze well!