Clean and peel the carrots and leeks, then grate them coarsely.
Boil the macaroni as directed on the package, drain and set aside.
Fry the bacon and set aside.
Melt the butter in a large saucepan over medium heat.
As soon as the butter has melted add the flour, stirring constantly.
Make sure there are no lumps in the mixture, then increase the heat a bit and start adding the milk a little at a time, still stirring constantly.
Let it simmer for a while before grating the Castello Tickler Mature Cheddar cheese and adding it to the mixture.
Warm the sauce thoroughly and then add the vegetables, bacon and macaroni, mixing everything well.
Pour the entire mixture into an ovenproof dish, sprinkle oatmeal/breadcrumbs on top and bake it in a preheated oven at 180 degrees for about 25-30 minutes.