Plunge the pasta into a saucepan of lightly salted boiling water. Return to the boil and simmer for 10–12 minutes until al dente. Drain well and return to the pan.
Meanwhile, heat a dry frying pan until hot, add the chorizo and cook for 3 minutes until browned and the fat is released. Remove from the pan with a slotted spoon. Add the onion and garlic to the pan and cook gently for 5 minutes until soft.
Stir in the macaroni with the chorizo, cream, stock and a little salt and pepper. Heat gently, stirring, for 2–3 minutes until warmed through. Stir in the Cheddar, remove the pan from the heat and stir until the cheese has melted.
Spoon the mixture into 4 x 300 ml (½ pint) baking dishes, sprinkle over the Parmesan and bake in a preheated oven, 190°C (375°F), Gas Mark 5, for 12–15 minutes until bubbling and golden. Serve with a crisp green salad.