The recipe Softened onions, a lovingly made sauce and some grated cheese is the perfect base in which to use up any leafy, thick-stemmed greens. Pour 500ml of milk into a saucepan, add a couple of bay leaves, 3 or 4 sprigs of thyme, half a dozen peppercorns and half a small onion. I like to stick a clove or two in as well. Bring almost to the boil then switch off the heat, cover with a lid, and leave to infuse for 20 minutes or so. Over a moderate heat, melt 35g of butter in a saucepan, stir in 35g of plain flour and stir for 2 or 3 minutes until the colour of a pale biscuit. Gradually ladle in the infused milk (I also add the aromatics in the pan), stirring constantly to remove any lumps, then stir in 100ml of double cream. Finely grate 65g of parmesan and stir into the sauce. Lower the heat so it simmers very gently for 20 minutes. Peel a red or white onion and slice it thinly, then do the same with 2 plump cloves of garlic. Warm 2 tbsp of olive oil in a frying pan, add the onion and cook over a low to moderate heat for 20-25 minutes, stirring regularly, until pale gold. Halfway through, introduce the sliced garlic. Set the oven at 200C/gas mark 6. Wash 350-400g of leafy greens, separating the stalks from the leaves. Cut the stalks into short pieces and add to the softened onions. Cover and let them cook in their own steam for 3 or 4 minutes. Add the leaves and turn them over with kitchen tongs until they start to wilt. Stir in the cheese sauce and, if you are not using a pan that can go in the oven, transfer to a 22cm ovenproof dish. Scatter a handful of grated parmesan over the surface and bake for 25 mins. The trick I keep a little plastic box of parmesan rinds in the fridge, adding them to minestrone or occasionally ragù. A lump of rind is a thoroughly good thing to add to the milk as it infuses. The twist Embellish the recipe with a scattering of flaked almonds before baking; you could also use pumpkin seeds or a mix of fresh, white breadcrumbs, parsley and finely grated lemon zest. Introduce snippets of bacon or salami to the softening onion, or a spoonful of chopped rosemary. Follow Nigel on Twitter @NigelSlater