Mackerel and bacon salad

INGREDIENTS

• 1 onion
• 3 tbsp white wine vinegar
• 500g/1lb small salad potatoes
• 2 tsp Dijon mustard
• 1 heaped tsp capers
• 2 tbsp white wine vinegar
• 6 tbsp olive oil
• 4 bushy sprigs dill
• 6 thin rashers smoked streaky bacon
• 2 whole smoked mackerel