1 tsp freshly grated horseradish (or 2 tsp horseradish sauce)
陆 lemon, juice only
spring onions, chopped
2 tsp Dijon mustard
freshly ground black pepper
100g/2陆oz unsalted butter, chopped
2 tbsp cr猫me fra卯che
2 whole smoked mackerel (or 4 fillets)
sourdough bread, cut into slices