Preheat the oven to 375°F (190°C or 180°C for fan ovens).
Heat 2 tablespoons of the oil in a frying pan over medium heat.
Sauté the leeks and red pepper for a minute or two until they are well coated in the oil.
Add the mushrooms and continue to sauté.
Grate in the garlic, add the thyme and pour the stock over top.
Cook, stirring occasionally, allowing the liquid to reduce a little.
Add the ketchup, mustard, parsley and crème fraîche (if using).
Cook gently for a few more minutes, stirring occasionally, until the sauce has thickened. (This will take longer if you omit the crème fraîche.)
Meanwhile, grate the parsnips into a bowl and toss with the remaining tablespoon of olive oil. Set aside.
Add the pepper and nutmeg to the vegetable mixture in the frying pan, stir through and taste for seasoning.
Divide the vegetable and mushroom mixture between four small pot pie dishes.
Pile the grated parsnips on top, leaving a little gap around the edges.
Drizzle with a little more olive oil.
Bake for 30 minutes or until golden.
Serve with peas, steamed green beans or a crisp, fresh salad.