Made this up today to feed a vegetarian friend. It also went down well with meat-eaters among the guests, and the 8-month-old baby present. Essentially, it's potatoes boulangere turned into a complete meal.
2lb of potatoes - or more or less to feed more/fewer people
1 or more onions
fresh or frozen spinach - if fresh, more than you think you need because it goes down to nothing
cheese - I used a mixture of mozzarella, goat's cheese and parmesan
milk and/or cream
Wash the spinach, then pan on a low heat with no additional water if you can help it. Cook it in batches if your pan is too small. When it has collapsed, squeeze out as much of the water as possible using a sieve, chop and reserve. Slice the potatoes thinly and store in a bowl of water to keep them from oxidising. Slice the onion thinly. Grate the cheese.
Heat the milk and/or cream and soft cheese/goat's cheese/other cheese in a pan until the cheese has melted. You could add an egg.
Butter a large shallow oven dish - or a smaller deeper one. Layer the potatoes, onion and spinach in the dish. You could put some grated cheese in one of the layers. Pour over the milk mixture. Sprinkle any remaining cheese on top.
Bake in the oven at 180C/gas mark 4 for 1 1/2 hours, approximately. It will look after itself.