Cut the chorizo into slices the thickness of a pound coin.
Put the onion and garlic in the bottom of a large roasting tin. Scatter over the chorizo, then add the chicken pieces, potato, rosemary and a couple of grinds of black pepper.
Drizzle with olive oil, then bake for 45 mins.
Halfway through the cooking time, give everything a good baste in the chorizo juices.