Grams change with the number of servings; the carbs in each serving stay the same.

Warm the oil in a pan and cook the cod and salmon over low heat for a few minutes; fish cooks fast.

Pour in the cream, add a little salt and pepper (and herbs if you like) and stir.

In a bowl, mash the boiled potato and celeriac together with the butter.

Spoon the fish into a small ovenproof dish and spread the mash over it.

Scatter the grated cheddar on top and brown it under the grill or in a hot oven.