Spray an 8" x 8" baking dish with a non-stick spray (Baker's Joy) and preheat the oven to 350 degrees.
Melt butter then blend in the sugar and vanilla.
Add 3 eggs, one at a time.
Whisk the dry ingredients together, then blend into the wet ingredients until well blended.
Stir in 1 cup of Reese's Peanut Butter chips until evenly distributed throughout the batter.
Pour into the prepared pan and bake for about 40-45 minutes. I baked it for 45 minutes. Since ovens cook differently, start checking middle with a wooden toothpick. It should be a little moist, but not gooey wet.
Place on a cooling rack and allow it to rest for 10-15 minutes before cutting into 16 squares.