Chicken, sausage and bacon puff pie

Ingredients

• 2 rashers of higher-welfare smoked streaky bacon
• 2 free-range chicken thighs (100g each), skin off, bone out
• 2 higher-welfare sausages
• 2 leeks
• 2 small potatoes (100g each)
• 2 tsp (heaped) English mustard
• 2 tbsp (heaped) plain flour
• 500 ml organic chicken stock
• 500 ml semi-skimmed milk
• 85 g watercress
• 1 tbsp olive oil (for brushing the rim of the pie dish)
• 320 g ready-rolled puff pastry
• 1 large free-range egg