For the mashed potatoes:

1 1/2 pounds potatoes
roughly 2/3 cup of milk
little knob of butter
salt, pepper, nutmeg

For the filling:

14 oz white fish, fresh or frozen
1 1/2 cup milk
2/3 cup vegetable (or fish) broth
1 1/2 cups green peas
1 small onion
3 cloves
1 bay leaf
1/2 tsp salt
1 large carrot
1 lemon
4 Tbs chopped flat-leaf parsley
cheese

For the white Sauce:

5 tbsp all-purpose flour
3 oz butter
1/2 a tsp salt
white pepper
white wine, optional