Francesinha (Porto Sandwich in Beer and Tomato Sauce)

Variations

• The sauce is the house. Porto restaurants do not publish theirs. That beer and tomato are the frame is uncontested; on top of that, whisky, port or brandy, milk or cream, meat trimmings and the amount of piri-piri all differ. The version above is a baseline, not an answer.
• How hot: tourist versions are mild and neighbourhood ones much less so. Halve the piri-piri or double it and it is still a francesinha (chilli and heat).
• Francesinha poveira: the Povoa de Varzim version, made flatter and wider so the sauce sits on it differently.
• Vegetarian versions are common in Porto itself: mushrooms and soy protein in the stack, and mushroom liquor in place of the beef stock (building umami).
• With or without the egg: both are served. The yolk running into the sauce pulls the heat back, so if you have made it hot, the egg is the balancing move.
• Its ancestor is the croque-monsieur: the accepted account is that Daniel da Silva brought the idea back to Porto in the 1950s from France, and the name means "little French girl". Set beside croque-monsieur, what got added is the sauce and the meat, wholesale.
• The same family: grilled cheese keeps only the cheese, and jambon-beurre takes everything else away. It has nothing in common with a hamburger beyond meat between bread.
• Other things served under melted cheese: French onion soup, lasagna.
• Same country: caldo verde, pastel de nata.

Tips

• The consistency of the sauce is the whole dish. Thick, it becomes a gravy sitting on the bread; too thin and it is soup. Aim for something that pools on the plate but still coats the back of a spoon — looser than cream, heavier than milk (thickening sauces).
• The cheese is a wall, not a lid. Melt it over the top and let it run down the sides. Anywhere the bread is exposed, the sauce goes straight in and it is porridge within five minutes.
• Sauce last, and hot. Poured in advance, the bread collapses before it reaches the table. Just short of boiling, over a plated sandwich, is how it is done (serving temperature).
• It has to be soft white bread. A crusty loaf repels the sauce and the whole filling pulls out in one bite. Sandwich bread takes the sauce up and still holds its layers.
• Cook the beer properly. Twenty-five minutes takes the harsh bitterness and the carbonation off a lager and leaves malt sweetness and a bitter finish. Cut short, that raw bitterness sits over everything else (cooking alcohol).
• Season the meat lightly. The sauce is salty, hot and rich; season the filling to match and one bite is as much as anyone wants (balancing flavour).
• Take no colour on the onion. The sweetness of browned onion pulls against this sauce. Soften it over a low heat and stop (browning).
• Make the sauce the day before. Overnight the beer's edge settles and the spice spreads. It is also the only part of this that can be done ahead.
• Do not brown the cheese. Left under the grill until it colours, the surface sets, and the sauce runs off it instead of soaking in. Stop it at the point where it flows (dairy and heat).
• Chips on the side. Chips sitting in the sauce are soft within a minute. Put them at the edge of the plate or in their own dish and dip (deep-frying).
• The leftover sauce is the useful part. It suits steak, potatoes and a fried egg the next morning; freeze it. It is very nearly reason enough to make this (reviving leftovers).
• It is a plate dish. Nothing about it assumes hands — not the height, not the amount of sauce. Knife and fork.