Potato Trout Gratin
Peel and slice the potatoes. Rinse the fillets under running water, remove the bones and cut into smaller pieces. Sprinkle with lemon juice. Rinse the celery, cut into thin slices and coarsely chop the leaves. Rinse the peas and halve diagonally. Alternately layer the celery, trout, peas and potatoes in a greased baking dish.
Mix the milk, cream and eggs. Season with salt and pepper. Add the broth and mustard. Mix well. Pour the sauce over the gratin. Coarsely crush the mustard seeds and sprinkle over the gratin. Cover the gratin with aluminum foil. Bake for about 30-40 minutes at 200°C (approximately 400°F). Fry the breadcrumbs in butter and spread over the finished gratin. Serve hot.