Stir together the peanut butter, eggs, and vanilla in a large bowl.
Stir in the brown sugar until combined. Add the baking mix and 3/4 cup of the dark chocolate chips, stirring just until moistened. Spread the mixture on a lightly greased jelly-roll pan.
Bake at 325°F until golden brown, 20 minutes. Remove from the oven, and sprinkle evenly with the remaining 11/4 cups dark chocolate chips; let stand until the chocolate melts, about 5 minutes. Spread the melted chocolate evenly over the top. Cut into pieces.
Recipes excerpted with permission from One Sheet Eats by Oxmoor House (Time Inc. Books, 2017)