Prepare a 9 by 9 inch baking pan by lining it with parchment paper, leaving excess hanging over the sides for easy removal later.
Brownie Batter
In a small pan over medium heat, melt butter and stir in sugar.
Remove from heat and stir in eggs and vanilla extract. Set aside.
In a medium bowl, mix flour, cocoa powder, salt and baking powder. Stir the butter, sugar and eggs into the dry ingredients until just mixed. A few lumps are okay.
Pour the brownie batter into the pan and set aside.
Peanut Butter Cookie Dough
In a medium bowl, whisk together vegetable oil and sugar. Then add the egg, vanilla extract, and peanut butter and mix well.
In a separate bowl, mix the flour, baking soda and salt and then add to the wet ingredients to form a dough.
Drop 25 scoops of peanut butter cookie dough (about 1 TB each) onto the brownie batter.
Bake for 27-30 minutes, then cool completely before cutting into bars.