Method

Preheat the oven to 180 C

Top and tail the leeks, slice in half lengthways and rinse until running water to clean. Cut the leeks in half cross wise

In a pan of boiling salted water, add the leeks and bring back to the boil. Cook the leeks for about 5 minutes, drain in a colander and then rest on paper towels to remove as much liquid as possible

In a saucepan, add the butter and start to melt and add the onions to the pan and start to soften. This will take about 5 minutes

Add in the garlic and cook for a further few minutes over a low heat. Then add the mustard, mix together and cook for another minute

Now add the flour and bring the mixture together and cook for a few minutes

Gradually pour in the milk and keep stirring as to remove lumps. The sauce should be looser/thinner than a standard white sauce. If you need more milk as it's too thick then gradually add some extra

Remove the sauce pan from the heat and add the grated Cheddar cheese. Stir until the sauce is smooth and thickened

Butter a baking dish large enough to hold the leeks and cheese sauce. Add the leeks and then pour over the cheese sauce to cover

Blitz the sliced bread in a blender to make fresh bread crumbs

Melt the butter in a saucepan and when melted, pour in the breadcrumbs, remove from the heat and stir until the butter has coated the breadcrumbs evenly

Sprinkle the breadcrumbs over the leeks and cheese sauce dish. Cover with tin foil

At this point you can keep the dish in the fridge until you’re ready later on in the day

To serve, heat the oven to 180C and cook the dish for 30 minutes