Ingredients
Method
- Preheat oven to 350°F (175°C). Line an 8-inch square metal pan with parchment. Stir cookie mix, melted butter, egg, and vanilla until a thick dough forms.
- Press dough evenly into the pan, smoothing the surface. Bake 18 to 20 minutes until edges are golden and center is set. Cool in the pan on a rack for at least 20 minutes.
- Beat softened butter, powdered sugar, 1 tbsp milk, vanilla, and salt for the frosting, adding more milk as needed. Spread over the warm bars and top with sprinkles.
- Lift out the slab, slice into 16 squares, and serve.
Notes
The bars are softest the day they are made, but they keep well in a covered container. If you double the recipe for a 9x13-inch pan, use the full 20 to 22 minute bake time and check the center with a toothpick before pulling the pan.
