Step 1

Heat the oil in a wide, heavy-based pan (with a lid) over a medium heat, add the onions and cook for 10 minutes until softened. Add the beetroot and cook for 5 minutes, then put the fish fillets on top of the vegetables in an even layer. Cook for 5 minutes more.

Step 2

Meanwhile, mix the crème fraîche, horseradish and yogurt in a bowl until smooth. It should be a fairly runny sauce so you might need to add 3-4 tbsp water to loosen.

Step 3

Slightly reduce the heat under the fish and pour the creamy yogurt mixture over the fillets. Cover with a lid and continue cooking for 8-10 minutes until the fish is just cooked through. Sprinkle over the herbs, grind over a little black pepper and serve with creamy mashed potato.