Preheat oven to 350F.  Spray the pan, and line an 8″ square pan with parchment, coating the parchment and sides of pan with butter or more cooking spray.

Make the Peanut Butter Swirl

1. In a medium bowl, stir all ingredients together until smooth.

Make the Brownie Batter

1. In a metal bowl over simmering water, melt the butter and unsweetened chocolate.  When a few bits remain, remove from the heat and whisk until fully melted and smooth.  You can do this in the microwave in 30-second segments if you wish, but I feel like doing it over the heat, I have a bit more control.
2. Whisk in the sugar, eggs, vanilla and salt. Stir in the flour using a flexible spatula or a spoon.

Assemble

1. Spread around 1/3 of the brownie batter over the bottom of the baking pan. Using a spoon, take dollops of the peanut butter swirl and scatter them on top of the layer of chocolate batter in the pan. They will fill up the space.  Then, intersperse the rest of the chocolate, also in dollops, trying to get it between the dollops of peanut butter swirl.
2. Using a butter knife, make swirls through the two batters, leaving nice ribbons of peanut butter swirl.
3. Sprinkle chocolate chips over the brownie batter.
4. Bake 30-35 minutes, until a wooden skewer or toothpick comes out almost clean.