500g potatoes, peeled and chopped
2 tbsp milk
1 tbsp olive oil
2 tsp creamed horseradish
Knob of butter, to serve
4 whole mackerel, cleaned with heads and tails on
Juice of 1 lemon
1 thumb fresh ginger, thinly sliced
1 large red onion, sliced
1⁄2 bulb fennel, thinly sliced
To make horseradish mash, cook potatoes in a pot of boiling water until tender. Mash potatoes with milk, olive oil and creamed horseradish. Season with salt and pepper. Add a knob of butter before serving.
Wash and dry mackerel with kitchen paper. Squeeze lemon juice over skin and flesh of mackerel, then rub with salt and freshly ground pepper. Fill fish cavity with ginger, onion and fennel. Tie up with cooking string.
Heat oven grill to high and cook mackerel for 5-6 minutes, without turning. Divide horseradish mash between four plates and serve whole mackerel on top.