Preheat oven to 350° and line an 8” by 8” ceramic baking dish with parchment paper.
In a large bowl combine flour, salt, and baking soda.
In a medium bowl stir butter, peanut butter, and brown sugar until combined. Whisk in egg until a silky mixture forms.
Fold dry ingredients and chocolate chunks into wet ingredients, reserving some chocolate for the top. Bake for 30 to 35 minutes until lightly golden brown around the edges. Cool for about 30 minutes.