Preheat oven to 350°F and line an 8” x 8” pan with parchment paper, or spray the pan with non-stick cooking spray.
Make the chocolate brownie batter by pouring the melted butter into a large bowl with the granulated sugar. Stir to combine and then add the eggs and vanilla extract.
Add the flour, cocoa powder, and salt to the bowl. Gently fold in the dry ingredients. Do not over mix the batter.
Mix the ingredients for the peanut butter brownie layer, by pouring the melted butter into a separate bowl with the brown sugar, granulated sugar and peanut butter. Stir until creamy and smooth.
Add the dry ingredients to the bowl and stir just until combined.
Spread the peanut butter layer on the bottom of the pan and top it with the chocolate brownie layer, spreading the batter for both layers out evenly.
Bake for 22 minutes. Brownies will still be soft and gooey, but will finish setting while they cool.