Layer the sweet potatoes and mealy potatoes in the prepared dish. Combine the cream and all the ingredients up to and including the pepper, pour over the top. Scatter over the cheese.
Approx. 40 mins. in the centre of an oven preheated to 200°C. Remove from the oven.
To prepare the fish
In a bowl, mix together the fish and all the ingredients up to and including the salt, spread over the potatoes, scatter over the almonds. Bake the gratin for approx. 10 mins. more.