1. Preheat your oven to 350°F (175°C). Line a 9×13-inch baking dish with parchment paper, leaving a 2-inch overhang on the long sides.

2. In a large mixing bowl, combine softened butter, brown sugar, and flour. Use a pastry cutter or fork to mix until the mixture resembles coarse crumbs with pea-sized butter pieces.

3. Press the crumbly mixture evenly into the bottom of the prepared pan, making sure to reach all corners and edges. Use your hands or the bottom of a measuring cup to pack it firmly.

4. Bake the crust for 15 minutes until the edges turn light golden brown and the crust feels firm to the touch.

5. While the crust bakes, chop your pecans into roughly 1/4-inch pieces, varying the sizes for better texture.

6. In a medium saucepan over low heat, combine sweetened condensed milk and chocolate chips. Stir constantly for 3-5 minutes until completely smooth and glossy.

7. Remove the chocolate mixture from heat and immediately stir in the chopped pecans until evenly distributed.

8. Pour the chocolate-pecan mixture over the warm pre-baked crust. Use an offset spatula or the back of a spoon to spread it evenly to all edges.

9. Return the pan to the oven and bake for 20-25 minutes. The topping should look set around the edges but still slightly soft in the center.

10. Let the pan cool completely on a wire rack for at least 2 hours, or refrigerate for 30 minutes for cleaner cuts.

11. Use the parchment overhang to lift the entire slab onto a cutting board. Wipe your knife clean between cuts for professional-looking edges. Cut into 24 squares or 36 smaller bars.