Our regular one -
Peel and boil potatoes, fry onions and garlic in big pan with lots of butter. Drain potatoes, tip into frying pan, mash. Add shedloads of strong cheddar and a pinch of mustard powder.
Spread in casserole dish, if going for the school dinner version, slice a tomato and dot it over the top. Bake until the edges are crispy.
But if you want more of a flan style one, shortcrust pasty, blind bake in a flan dish.
Slice onions into rings, fry. Dice or scallop potatoes (your choice), boil.
Layer onions and potatoes in flan base.
Take half a dozen eggs, milk or cream, and a shedload of cheddar. Mixed herbs too. Whisk all together, pour over the onion and potato.
Bake until set.