It's a tried-and-tested recipe – but leeks give this classic a new edge.
Cooking time: 30 mins
3 tbsp (40g) butter, plus extra for buttering the dish
2 leeks, cleaned and sliced
3 tbsp (40g) plain flour
1 pint milk
150g strong cheddar cheese (lancashire or red leicester are also good options), grated
350g penne or rigatoni
Salt and pepper
Cut the butter into chunks and melt in a medium nonstick saucepan. Add the leeks, stir and leave them to cook for 5 minutes until soft. Remove the pan from the heat and stir the flour into the leeks with a wooden spoon. Put the pan back on to a low heat for just a few seconds to cook the mixture, stirring all the time, then remove from the heat again. Add the milk a little at a time, stirring it in completely before adding more (don't worry if it gets thick) but save 50ml of milk for later. Put the pan back on the hob and gradually bring the milk to the boil, stirring all the time, then turn the heat right down and leave to simmer for 5 minutes, stirring occasionally. Meanwhile, bring a large saucepan of water to the boil then cook the pasta for the time instructed on the pack. Just before the pasta is ready, stir half the cheese into the sauce and season with salt and pepper. Add the remaining milk now if it looks too thick. Drain the pasta, tip it into a pre-buttered shallow baking dish, pour over the cheesy leek mix and stir well. Sprinkle the remaining grated cheese over the top and place the dish under a hot grill for 5 minutes or so until the top is brown and crispy. If you don't have a grill, bake in the oven at 200C/gas 6 for 15-20 minutes.