Cheesy potato patchwork pie

Method

• step 1

  Start by making the pastry. Tip the flour and butter into a large bowl along with ½ tsp finely ground black pepper. Rub the butter into the flour using your fingertips until it resembles fine breadcrumbs. In a jug, whisk together the whole egg, yolk, milk and thyme leaves. Pour three-quarters of the egg mixture into the flour crumbs, stir it in using a cutlery knife, then bring it together using your hands into a smooth disc and chill for 30 mins.

• step 2

  Tip the potatoes into a saucepan, cover with cold water and add a generous sprinkling of salt. Put the lid on, bring to the boil, then reduce to a simmer and cook for 7-9 mins until almost tender – a sharp knife should slide in easily. Drain well and set aside to steam-dry.

• step 3

  Heat the oil and butter in a frying pan over a medium heat. Stir in the leeks, garlic, thyme and bay with a pinch of salt and pepper. Cook for 20-22 mins until softened. Mix in the flour and mace and cook for a couple of minutes before stirring in the mustard. Remove from the heat and season to taste. Slowly pour the milk in, stirring well, before mixing in the parmesan and cheddar. Warm over a low heat until the cheese has melted. Remove the bay leaves and thyme sprigs. Butter a 25cm round, ovenproof dish and arrange the potatoes on the bottom. Pour over the leek mixture and set aside to cool to room temperature. Will keep covered and chilled for up to 24 hours.

• step 4

  Lightly dust a clean work surface with flour and roll out the pastry to around 1/2cm thick – you don’t need to be too precise. Cut into small rectangles, around 3 x 6cm, and arrange the rectangles over the top of the pie haphazardly, making sure they mostly overlap, leaving some steam holes, until the pie is completely covered. Will keep frozen, unbaked, for up to two months. Defrost in the fridge overnight before baking.

• step 5

  Heat the oven to 220C/200C fan/gas 7. Brush the remaining egg over the top of the pie and bake in the oven for 30-35 mins. Remove from the oven and leave to rest for 10 mins before serving with steamed greens or a watercress salad, if you like.