This is adapted from several recipes. Many call for smoked fish, of which I can only find salmon. Some also call for shrimps. Some mix the cheese with the mashed potatoes and some use peas. I find it´s a lot of trouble to make mashed potatoes just for this, but it´s a great way of using them up if they´re leftover.
I used cazón, which turns out to be school shark and lately Greenpeace has declared it unsustainably fished, so I won´t be buying it any more. Too bad, it was tasty and cheap. Sorry - forgot to take pics.
500 gr. white fish - I use chunks but you can use fillets
1/2 medium onion finely sliced
2 cups grated cheese
2 cups mashed potatoes
2 cups milk
fresh ground pepper
1 tbsp. tarragon
3 tbsp. butter
2 tbsp. flour
2-3 cloves garlic, minced
Poach the fish in the milk with the salt and pepper. Drain - retaining milk. Melt butter in a saucepan, add garlic and tarragon and sautee for a few minutes. Add flour and cook another couple of minutes. Add milk, bring to a simmer until it thickens. Meanwhile, butter a cassarole dish and layer the onion in the bottom with the cooked fish on top, followed by the grated cheese. After the white sauce has thickened, pour on the top. Finish with the mashed potatoes spread evenly.
Bake in a 400 F/ 200 C oven for 40 minutes or until brown.