"Why this recipe works:Butterscotch is made by cooking brown sugar and butter together, but simply adding those ingredients to our icebox cookie dough wasn’t enough to make a convincingly butterscotch-y cookie. Exchanging dark brown sugar for light helped but not enough. Butterscotch chips are a potent source of butterscotch flavor—just 1/2 cup was plenty—but left whole, the chips made the cookies impossible to slice neatly. Melting the chips down and creaming them with the butter was the trick to bold butterscotch flavor and a smooth, sliceable dough...."