Tortilla de patatas

Square off a side of each potato and slice across every eighth inch, by knife or mandolin.

Slice the onion across the grain so the pieces break down and melt.

Whisk the five eggs with salt, black pepper and cayenne very thoroughly until no white is visible.

Heat a third of a cup of olive oil in a large non-stick skillet over medium-high; add the potatoes, onions and a big pinch of salt.

Cook about 15 minutes, covered for two or three minutes at a time and then tossed, until the potatoes are fully tender and breaking apart; brown as far as wanted.

Transfer into the eggs and stir together with a spatula; cover and let sit about five or 10 minutes.

Pour into a smaller nonstick pan (8 to 10 inches; just over nine used) over medium-high heat, smooth the top and cook, covered, about four minutes until the bottom is browned and the eggs set.

Slide onto a plate, cover with a second plate, flip, and slide back into the pan.

Cook the other side a minute or two, depending on how soft the inside should be.

Transfer to a serving plate and slice.

Serve with garlicky aioli topped with a sprinkle of cayenne and chopped parsley.

Variation: for tapas, cut into one-inch squares, top with a touch of aioli and spear each with a toothpick.