One of the most classic and popular of all Spanish dishes, the egg and potato tortilla is, simply, iconic. It was, fittingly, the first dish I learned to make when I moved to Spain in 1996, in a lesson given to me by my future brother-in-law, Robert. Preparing a tortilla with potato alone is fine, but using an equal amount of onions produces a sweeter, moister, and, in my mind, superior result. While the key to a good tortilla is keeping it moist in the center, the real trick, he showed me, comes in flipping it. Or rather, flipping the tortilla without the bottom sticking.