Smoked Haddock Gratin Recipe with Ham

Ingredients

• 400g potatoes peeled and cut into 1/2 cm slices
• 1 onion finely sliced
• 1 stick celery finely sliced
• 1 tbsp butter plus more for the dish
• 1 tbsp plain flour
• 200ml chicken or veggie stock
• 200ml half-fat crème fraîche
• 150g skinless smoked haddock cut into chunks
• 100g cooked ham diced
• chopped to make 2 tbsp flat-leaf parsley
• green salad to serve