Asparagus fish

Skin the fish while it is still frozen and defrost slightly. Season to taste with salt and pepper and place in a microwave bowl. Sprinkle the chopped onion on top. Drain the asparagus spears, reserving the liquid. Arrange the asparagus on top of the fish. Blend the asparagus liquid, milk, mustard powder and cornflour in a glass jug. Season to taste with salt and pepper. Microwave for 3-4 minutes on 100 per cent power or until the mixture just comes to the boil. Stir frequently. (Add extra milk if the mixture is too thick). Add the Cheddar cheese and stir until completely melted. Pour over the fish. Cover and microwave for 12-14 minutes on 100 per cent power or until the fish is done. (The cooking time will vary, according to how much the fish has defrosted). Serve with potatoes, peas and courgettes.