Pepparrotssås (horseradish sauce) with pickled herring and hot-smoked salmon

Ingredients

• 200ml crème fraîche
• ½ tsp caster sugar
• ¼ tsp salt
• 1 small crushed garlic clove
• 1 tsp cider vinegar
• 2cm piece grated horseradish root
• 150g pickled herrings and their onions
• hot smoked salmon (we like RR Spink & Sons Sweet Scottish Herring Fillets and Korshags Hot Smoked Salmon, both from Ocado)
• 2 tsp chopped red onion
• Salmon roe (optional)
• Few springs of dill