Cut the mackerel into pieces, remove the bones.
Cut the potatoes into circles and dip in boiling water for 5 minutes, then drain the water and season to taste.
Put half the potatoes on the bottom of a slightly greased form, grease with mayonnaise and arrange the fish.
Salt and pepper and grease with mayonnaise again.
Put the rest of the potatoes on top of the fish and grease with mayonnaise.
Sprinkle the casserole with grated cheese. Bake in the oven at 190 degrees 40 minutes.
Potato casserole with mackerel is ready, cut into portions and serve.