Preheat the oven to 200C/400F/Gas 6. Parboil the sliced potatoes in salted boiling water for a few minutes until softened, then drain in a colander.
Place a 20cm/8in casserole-style pan on a low heat, and add the oil, garlic, onion, fennel and fennel seeds. Cook slowly for 10 minutes with the lid on, stirring every so often.
Take the pan off the heat. Lay the trout fillets skin-side up over the onion and fennel.
Mix together the cream, parmesan and anchovies, season with salt and freshly ground black pepper, and pour over the fish. Toss the potato slices in a little olive oil, season with salt and pepper and layer these over the top.
Place in the oven for 20 minutes, sprinkling with the breadcrumbs and a little grated parmesan five minutes before the end. Serve with lemon halves, a green salad and cold beers!