In French au gratin is a cheese-topped dish. If you cook something au gratin, you cover it with sauce, top it with cheese (or sometimes breadcrumbs) and brown it under the grill or in the oven. A huge variety of savoury dishes can be cooked au gratin; the most common are vegetable dishes.
-Boil or steam vegetables (broccoli is a good choice) until just tender and put in a gratin dish (a low-sided oven-proof dish).
-Make a sauce by blending 1oz (25g) flour with 1oz butter over a low heat, slowly adding half a pint (300 ml) of milk and stirring continuously (increase the heat to thicken) till the sauce is thick and creamy. Add grated cheese, French mustard or whatever flavouring you want, and melt in.
-Pour the sauce over the vegetables, grate over enough strong cheese to cover (Cheddar or Lancashire, for instance) and cook under a grill for 5-10 minutes until golden, or 20 mins in the oven at 200 degrees.