Preheat oven to 350 degrees F. Spray an 8-inch square baking pan with non-stick cooking spray. See note*

Combine the flour, salt, baking powder, and grated nutmeg in a bowl and whisk to combine.

In another mixing bowl, whisk eggs. Add brown, cooled melted butter, and vanilla. Whisk until smooth.

Add peanut butter and whisk until smooth.

Remove 1 tablespoon from the flour mixture and toss with peanut butter and chocolate chips.

Add flour mixture to wet mixture and stir with a wooden spoon until combined.

Add peanut butter chips, chocolate chips, and chopped Reese’s cups and stir gently to combine.

Transfer mixture to prepared baking pan and smooth.

Bake until set and golden on the edges, about 30 minutes. Do not overbake.

Let cool completely before cutting into squares.