Creamy Cheesy Mushroom and Leek Pie

Meanwhile, trim the root and the dark green leafy part from the leek. Halve lengthways then thinly slice widthways. Grate the cheddar cheese. 

Heat a drizzle of oil in a large high sided frying pan on medium high heat. Once the oil is hot, add the mushrooms and leek with a pinch of salt and pepper, stir fry until golden, 4-5 mins. Stir in the wild mushroom paste and water (see ingredients for amount) and cook until thickened, 2-3 mins.

Stir in the mustard, and half the creme fraiche. Bring it to a boil, and bubble until piping hot, 1-2 mins. Taste and season with salt and pepper if needed. Transfer the mushroom and leek mixture into an ovenproof dish. Mash the potatoes until smooth, then, stir in the remaining creme fraiche and one third of the cheese. Season with salt and pepper. Top with an even layer of the creamy mash, then scatter over the remaining cheese.

When the oven is hot, bake on the top shelf until the cheese is melting and bubbly, 10-15 mins. Meanwhile, wipe the frying pan clean. When there are 2 mins left for the pie, pop the empty frying pan on medium-high heat with a drizzle of oil. When the pan is hot, add the peas and stir-fry for 2-3 mins.