Potato, Leek and Cheese Pie Recipe | Mary Berry Everyday BBC2

Ingredients

• 125g butter
• 125g lard
• 350g plain flour, plus extra for dusting
• 1 egg, beaten, for brushing
• 60g butter
• 2 small leeks (about 150g/5oz each), thinly sliced
• 1 onion, thinly sliced
• 450g potatoes (about 2 medium), peeled and cut into 2cm (¾in) cubes
• 600ml milk
• 50g plain flour
• 1 tbsp Dijon mustard
• 1 tbsp chopped thyme leaves
• 50g mature Cheddar cheese, grated
• 50g Parmesan cheese, grated
• Salt and freshly ground black pepper