This is a Nigel Slater recipe I found in an ancient magazine… and it’s really good! I only changed a couple of things 1. I never have any stock, so I cooked it in wine and water 2. Mr Slater added tarragon too but I couldn’t find any.
Gently cook the finely chopped whites of four large leeks in butter and oil for about 10 minutes (or until soft). Removing the leeks, now cook a big handful of roughly chopped mushrooms (any type will do, cheapy cheapy button mushrooms or, if you’re lucky like me, any funky ones in season). Once the mushrooms are cooked add the leeks, the zest and juice of one lemon, 2 heaped tablespoons of flour, 4 teaspoons of Marsala powder, salt, pepper and 300ml of a mixture of white wine and water. Give it all a good stir and leave to simmer for a few minutes. Add in 2 massive tablespoons of Creme Fraiche and remove from the heat. Transfer into a oven dish and top with mashed potato (boiled skins on, mashed with lots of butter and salt). Cook for 30 minutes at 180degrees or until potatos are brown and the sauce is bubbly.