I’ve made these so many times, so you won’t have to. On the surface this seems like a dead-simple recipe, but it took quite a bit of tinkering to nail. Tahini has a complex molecular structure made up of lots of tiny carbohydrate molecules that cling to liquid for dear life, seizing up the way chocolate does if you add liquid to it at the wrong time. But if you play your carbs right and add the tahini last, after all of the other ingredients, it stirs in smoothly and bakes up into these sexy little squares that get better as they sit around. To make these non-dairy, swap in a neutral-flavored olive oil or vegetable oil instead of the butter.