Pre heat your oven to 220C / 200C fan / gas mark 7 / 425F.
Meanwhile, heat a wide, oven proof saucepan or cast iron casserole dish over a medium heat and add the olive oil and chorizo. Cook for 3 minutes, stirring frequently. Tip the chorizo onto a plate.
Turn down the heat and add the butter to the pan you just used for the chorizo. When the butter is melted add the onions and fry with the lid on for about 3-4 minutes, until the onions are nicely softened. Add the garlic and fry for 1 more minute. Stir occasionally.
Sprinkle the plain flour over the onions/garlic and stir well, then add the milk very slowly, stirring constantly until thickened. When the sauce is roughly the thickness of double (heavy) cream, add in a few twists of black pepper, the chorizo and 150g/5oz of the cheddar cheese. Stir until the cheese is melted and then turn the heat off.
Tip the macaroni into the cheese sauce, together with about a tablespoon of the cooking water, and stir to combine. Scatter the panko topping evenly over the top and place in your preheated oven for 10-15 minutes or until golden and bubbling.
If you don’t own an oven proof saucepan or cast iron casserole dish, simply use a regular pan and transfer the macaroni cheese to an ovenproof dish before adding the panko topping. You may find you need to cook the macaroni cheese for a little longer as a result.
Nutrition information is approximate and meant as a guideline only.