1-First, preheat your oven to 350°F (175°C) and prepare a baking pan by greasing it or lining it with parchment paper for simple cleanup.

2-In a bowl, mix the 2 cups all-purpose flour, ½ cup packed light brown sugar, and ½ teaspoon salt. Cut in the 16 tablespoons of softened unsalted butter until it forms coarse crumbs, then add ½ cup chopped pecans or walnuts for a nutty texture.

3-Press about two-thirds of this crumb mixture into the pan to form the base layer, which will bake into a buttery crust.

4-For the filling, melt the 1 cup bittersweet chocolate chips with the one 14-ounce can of sweetened condensed milk, then spread this rich mixture over the crust evenly.

5-Add dollops of ½ to ⅔ cup raspberry preserves on top, followed by sprinkling the remaining crumb mixture, along with 1 cup semi-sweet chocolate chips, to create the crunchy topping.

6-Bake the bars for 25 minutes until they are set and the top turns golden. Remember to cool them completely before cutting to keep their shape and layers intact.

7-For adaptations like quick breakfast treats, you can tweak the recipe slightly, but always let the bars cool fully for the best results.