Peanut Butter Meets Gooey mores in a Cookie Bar

Ingredients

• 1 cup (227 g) unsalted butter softened
• 1 cup (235 g) creamy peanut butter I don't recommend using natural peanut butter
• 1 cup (200 g) light or dark brown sugar tightly packed
• 1 cup (200 g) granulated sugar
• 1 large egg + 1 large egg yolk
• 1 ½ teaspoons vanilla extract
• 2¾ cups (345 g) all-purpose flour
• ½ cup (65 g) graham cracker crumbs
• 1 teaspoon baking powder
• 1 teaspoon cornstarch
• ½ teaspoon salt
• 2 Tablespoons milk
• 7 1.55 oz milk chocolate Hershey bars chopped into pieces* or 2 cups milk chocolate chips (340g)
• 1 ½ cups (72 g) mini marshmallows