For these easy bar cookies, top a shortbread cookie crust with miniature candy bars and bake in the oven until the candy melts into a yummy caramel and chocolate topping.
1. Heat oven to 350 degrees F. Line an 8 x 8 x 2-inch baking pan with heavy-duty or nonstick aluminum foil, making sure the foil is tucked into all the corners and that there is at least 1 inch overhanging the top of the pan on all sides.
2. Combine flour, confectioners sugar, cornstarch and salt in a medium-size bowl and with an electric mixer, mix on low speed. Add butter and mix on low speed until ingredients just begin to come together. Sprinkle mixture across the bottom of the prepared pan and press with your fingertips into an even layer (mixture will be dry). Place the pan in the freezer for 15 minutes.
3. Bake crust at 350 degrees F until the edges are just golden, 18 to 20 minutes. Remove the pan from oven to wire rack.
4. Place the candy bars in 4 rows of 5 over the hot crust and return pan to the oven. Bake for 10 more minutes, remove the pan from the oven and then spread the melted candy into an even layer with an offset spatula. Bake an additional 5 to 6 minutes until the candy is melted and bubbly. Transfer the pan to a wire rack and let cool completely.
5. Grasping the overhanging foil on either side of the pan, lift the bars from the pan and place on a cutting board. Use a sharp chefs knife to cut into 20 pieces. Keep at room temperature in an airtight container for up to 3 days.