Potatoes, tomato and cheese casserole

This is another winning improvisation, sort of a clean out the fridge recipe :-) It is substantial enough to hold up as a main dish, or also as a side with other pasta or rice dish in smaller portion. The handy thing about this dish is all the ingredients are the items you usually have around in the kitchen. You can always experiment with different type of cheese, anything that melts well in the heat will be great in this dish!

4 onions, sliced thin
50g butter
5-6 large tomatoes, ripe yet firm enough thickly sliced
potatoes, 3 large or 5-6 medium
150g fontina cheese, chopped
100g Parmigiano reggiano or grana padano, grated
1 cup full of bread crumbs
salt and pepper to taste
mild paprika
2-eggs-beaten
200ml. sour cream or creme fraiche

Sautè the onions in butter.
Peel and slice the potatoes about 5mm thick, boil or steam to the point they are still fairly firm, just a few minutes.
Prepare a mixture of the chopped, grated cheese, sautèed onion and bread crumbs, salt, pepper and mild paprika.
Butter a baking dish (about 20X30cm, not too shallow) and put in a layer of potatoes on the bottom, then another layer of tomatoes over the potatoes. Cover the surface with the cheese/onion/bread crumb mixture.
Repeat layering til you've used all ingredients, ending with the mixture on top.
In small bowl beat the eggs and sour cream til smooth, pour over to cover the surface.
Sprinkle on a little more paprika for colour.
Cover and bake at 190° for 30 min. Uncover and bake 15 min longer so it will puff and get golden.