Peanut Butter Reese's Cup Brownies

I had decided to double this recipe.  It turned out good but I was suggest not doubling it and instead baking the quantity for two separate 8x8 pans as the original recipe reads.  The reason being is that when you go to pull the bars out of the pan as directed, it is too dense and the bars crack down the middle.  It just isn't as pretty of a presentation then because you're not able to cut the bars into pretty squares.  I'll give the recipe based on how I will do it next time!

1/2 c butter
3/4 c all purpose flour
1/4 c unsweetened cocoa powder
1/2 tsp baking powder
1/2 tsp kosher salt
6 oz semi sweet chocolate, chopped
1 c sugar
2 large eggs
1 tsp vanilla extract
8 Reese cups, chopped

Heat oven to 350 F.  Grease an 8x8 inch with shortening.  Line with 2 crisscrossed pieces of parchment paper, greasing in between and leaving an overhang on all sides.  Grease the top of parchment paper as well.
In a medium bowlm whisk together flour, cocoa powder, baking powder, and salt.  Set aside.  In a large microwave safe bowl, combine chocolate and butter.  Microwave on high for 30 second intervals, stirring between each, until melted and smooth.  Let cool slightly and whisk in sugar, eggs, and vanilla, stirring until smooth.
Add flour to the mixture and mix until just combined (do not overmix!).  Fold in Reese cups.  Spread batter into prepared pans and bake until a toothpick comes out clean  when inserted into the center, about 30-35 minutes.  Let cool completely in the pan before using the overhang of parchment to pull the bars out and cut into 16 squares.