Yes, you can have your brownie, shortbread and caramel and eat it, too. Wait, that's not how that goes?
1 1/2 cups (3/4 lb.) butter
2 1/2 cups all-purpose flour
1 1/4 cups sugar
2 tablespoons cornstarch
12 ounces individually wrapped soft caramels, such as Kraft
1/4 cup whole milk
10 ounce bittersweet or semisweet chocolate, finely chopped
3 large eggs
1 tablespoon vanilla
1/2 teaspoon baking powder
1/4 teaspoon salt
How to Make It
Cut 1 cup butter into chunks. In the bowl of a food processor, combine 2 cups flour, 1/2 cup sugar, cornstarch, and the butter chunks. Whirl until dough comes together. Press evenly over the bottom of a buttered 9- by 13-inch baking pan. Bake in a 325° regular or convection oven until top feels dry and is just beginning to brown, about 25 minutes. Let cool completely.
Meanwhile, unwrap caramels and place in a microwave-safe bowl with milk. Cook in a microwave oven on full power (100%) for 1 minute. Stir mixture, then cook and stir at 30-second intervals until melted and smooth, about 3 minutes longer. Spread caramel mixture evenly over cooled crust and chill until firm, about 20 minutes.
In a large bowl set over a pan of barely simmering water (bottom of bowl should not touch water), stir chocolate and remaining 1/2 cup butter often until melted and smooth. Remove bowl from over water and, with a whisk or a mixer on medium speed, beat in remaining 3/4 cup sugar, eggs, and vanilla until well blended. Stir in remaining 1/2 cup flour, baking powder, and salt until well blended.
Pour chocolate mixture over caramel layer and use a knife or spatula to spread level, completely covering caramel.
Bake in a 350° regular or convection oven until a wooden skewer inserted into the chocolate layer comes out clean, 35 to 40 minutes. Let cool completely, then cut into 24 bars.