Preheat your oven to 350°F. Line the bottom and sides of a 13×9-inch baking pan with foil.

First, make the crust: In a medium bowl, whisk together flour, 1/2 cup granulated sugar, and 1/2 teaspoon salt. Add 1 cup melted butter; use a spatula or a wooden spoon to stir the butter into the flour mixture until a soft dough forms.

Crumble and press the dough evenly into the bottom of the prepared baking pan. Bake for 25 to 30 minutes or until the crust is baked through and the edges are lightly golden. Set aside to cool slightly.

Meanwhile, make the filling: In a large saucepan over medium-low heat, use a spatula or wooden spoon to stir together sweetened condensed milk, brown sugar, 1/4 cup granulated sugar, heavy cream, corn syrup, and 1/2 teaspoon salt. Add 1/2 cup butter. Stir mixture constantly over medium-low heat for about 15 to 20 until mixture bubbles, thickens, and turns to the consistency and look of melted peanut butter (an instant-read thermometer inserted in the mixture should read between 235°F and 240°F). Remove the mixture from heat; pour and spread evenly over the shortbread crust in the pan. Set aside to cool and set for 1 1/2 hours.

Finally, make the chocolate topping: Add chocolate chips and shortening to a large, shallow, microwave-safe bowl. Heat chocolate on High for 20 seconds. Stir, then continue to heat on High in 20-second increments until chocolate is fully melted and smooth.

Using two forks, roll each bar in melted chocolate to coat; transfer to a sheet of wax paper or a cooling rack to set. Pipe or drizzle extra chocolate over tops of bars, if desired. Transfer bars to refrigerator; refrigerate for at least 30 minutes, or until chocolate is fully set.