Sardine hand pies with cornichons and paprika

Ingredients

• 2 x 120g tins sardines in oil, drained
• 1 medium potato (about 150g), finely diced
• ½ red onion, finely chopped
• 40g cornichons, finely chopped
• 1 garlic clove, finely grated
• 2 tsp sumac or 1 tsp finely grated lemon zest
• 1 tbsp smoked paprika
• 1 tbsp rapeseed or olive oil
• Plain flour to dust
• 500g block all-butter puff-pastry
• 1 free-range egg, lightly beaten
• Nigella and/or sesame seeds to sprinkle