‘Weeknight staple’: Just 4 ingredients. I don’t even glance at a recipe anymore.

Place the pan on a wire rack and let the bars cool completely in the pan—this helps them set and slice cleanly. Once cool, use the parchment overhang to lift the slab out of the pan and transfer it to a cutting board. Cut into 12 bars (or smaller squares, if you prefer). Store in an airtight container at room temperature for up to 3 days, or refrigerate for a slightly firmer, chewier texture.

Because this recipe is so streamlined, it’s an easy canvas for small tweaks. For a nutty version, fold in 1/2 cup of chopped toasted walnuts or pecans along with the chocolate chips; the crunch and slight bitterness help balance the sweetness of the condensed milk. If you like a sweet‑salty contrast, sprinkle a pinch or two of flaky sea salt over the bars as soon as they come out of the oven so it adheres to the surface. You can also swap the semisweet chips for milk chocolate, dark chocolate, or a mix, keeping the total amount the same. For a subtle flavor upgrade, stir 1 teaspoon of vanilla extract into the butter–condensed milk mixture (this technically adds a fifth ingredient, but it has an outsized impact on aroma and depth). If you prefer thinner, crisper bars, bake the dough in a 9×13-inch pan and start checking for doneness around 15–18 minutes. Finally, for easy freezing, cut the cooled bars, wrap them individually, and freeze for up to 2 months; they thaw quickly and are excellent slightly chilled.