Wash and dry the fish fillets, then cut into pieces. Drizzle with juice from the lemon.
In a bowl, mix the tomato paste, egg yolk, and 1-2 cups cream together until smooth.
Finely chop the onion and mince the garlic clove, then add them to the cream mixture. Season with 1 teaspoon hot paprika, 1 teaspoon Italian herbs, salt, and pepper to taste.
Place the fish pieces in a greased baking dish. Pour the sauce over the fish and stir gently to combine.
Sprinkle the grated cheese evenly over the sauce and dot with small pieces of butter.
Bake in a preheated oven at 210 °C (410 °F) for 25 minutes, until the fish is opaque and flakes easily and the cheese is golden brown on top.