陆 cucumber, peeled, thinly sliced on a mandoline
4 tbsp grated fresh horseradish
陆 small lemon
1 small red onion, thinly sliced
2 tsp English mustard powder
salt and freshly ground black pepper
salt
knob of butter
2 heaped tablespoon cr猫me fra卯che
4 fresh mackerel fillets
4 slices soda bread, toasted, buttered