In a small, dry skillet, roast the garlic cloves and chile over medium heat, turning regularly, until they’re soft and splotchy black in places, about 5-10 minutes for the chile, 15 minutes for the garlic. Finely chop the garlic and chile. Scoop into a large bowl.

While the garlic and chile are roasting, measure the sesame seeds into another small skillet and set over medium heat. Stir until they are fragrant and golden, 4-5 minutes. Cool.

Cut the avocados in half, remove the pit then scoop the flesh from each half into the bowl with the garlic. Measure the tahini into the bowl, along with 1 tablespoon of the toasted sesame seeds. With an old-fashioned potato masher, a large fork or the back of a large spoon, coarsely mash the avocado with everything that’s in the bowl, mixing it evenly.

Scoop the chopped onion into a strainer, rinse under cold water, shake off the excess and add to the bowl. Gather the watercress leaves together and slice them thinly into a chiffonade. Add them to the bowl, along with the lime juice. Stir gently to combine, then taste and season with salt, usually about 1 teaspoon. Cover with plastic wrap pressed directly on the surface of the guacamole and refrigerate until you’re ready to serve.