Peanut Butter Blondies

or 170g) unsalted butter, melted and slightly cooled for 3 minutes

packed light or dark brown sugar

creamy peanut butter

large eggs + 1 extra egg yolk

pure vanilla extract (yes Tablespoon!)

all-purpose flour (spoon & leveled)

baking powder

salt

and 1/4 cups Reese's Pieces