Preheat the oven to 350 and prepare an 8x8-inch pan with parchment paper. Set to the side.
In a large bowl, whisk together the brown sugar, egg, vanilla, salt, butter, and peanut butter. Whisk until combined.
Fold in the flour and cornstarch. The dough is combined when it is streak-free of the dry ingredients.
Mix in the peanut butter and chocolate chips, making sure they are distributed evenly.
Add the blondie dough to the pan using a rubber spatula. Top the blondies with any extra peanut butter and chocolate chips.
Bake in the oven for 35 minutes. Let the blondies cool in the pan.