Leeks, cheese, bread - Telegraph 2 medium leeks (about 350g untrimmed weight), trimmed, washed and sliced 2 thick slices of sourdough or other robust bread 50g strong Cheddar, grated Melt the butter in a medium saucepan over a medium heat, then add the leeks. As soon as they are sizzling, turn the heat down quite low and put the lid on the pan. Sweat gently, stirring often, for about 10 minutes, until the leeks are tender. Season with salt and pepper to taste. Preheat the grill. Toast the bread (or not, if you prefer). Spoon the leek mixture thickly over the bread and top with the grated cheese. Grill until bubbling and golden, then serve straight away. Plus one A few thyme leaves, stirred into the leeks as they are sweating, will enhance the flavour. A smear of mustard on the toast is delicious too. Swaps You can also make a fine version of this with red onions in place of the leeks: finely slice 2 medium red onions and cook them gently in butter for at least 20 minutes until very tender. Lightly fried mushrooms also work very well in a cheesy open toastie like this, in addition to - or instead of - the leeks.