Everything into the pan
High heat to start. Coat the bottom of a wide pan with olive oil, halve the yellow onion and cut it into big cubes — the whole lot gets blended later, so there is no point being neat about it. Wait until the onions are soft and translucent. In goes the tomato pulp, then the beer, then the piece of pork fat with the skin still on it: the skin is where the body of the sauce comes from, so do not trim it off. Piri piri to your liking — this is where the heat is decided — and a pinch of salt.