Add the potatoes to a pot of boiling water with a pinch of salt and cook for 10-15 minutes until soft.
Heat a little oil in a large pot and add the carrots, leek and onion and cook for a couple of minutes until softened then add the mushrooms and garlic and cook for a few minutes longer.
Add the tomato puree, flour and thyme followed by the stock and wine. Bring to a simmer and cook for about 10 minutes until the sauce is thickened.
In the meantime mash the potatoes with milk and butter and a sprinkling of salt and pepper until the texture is to your liking. I would try not to go too sloppy here so that it doesn't mix with the sauce when you top the pie.
Pour the vegetables into an ovenproof dish and top with the mashed potato. Gently spread the potato with the back of a spoon until it coves the whole pie. Drag a fork across the top to add a pattern if desired.
Place under a medium-high grill (broiler) for 10-15 minutes until browned and crispy.
Nutrition information is an estimate and will vary depending on the exact ingredients used.