- Drop the potato, turnip or rutabaga, and ½ parsnip in a saucepan of rapidly boiling water.
- Bring back to the boil, and simmer until potato is soft (about 20 minutes).
- When cooked, drain off the water, add the margarine, and mash until creamy smooth.
- Set aside.
- Reconstitute the TVP by mixing the TVP, boiling water and marmite. Let sit.
- Put olive oil in a saucepan over medium heat, then add the leek, garlic and carrot and ½ parsnip. Sauté until the carrot is soft.
- Add the mushrooms and cook a minute or two more.
- Add the flour and stir like mad for a solid 30 seconds. Still stirring, add the TVP and its soaking broth to soak up the flour and thicken.
- Add the mustard, ale and some black pepper. Stir to mix all very well. Simmer for about 10 minutes to thicken the sauce.
- Pour into a casserole dish, top with the potato/rutabaga/parsnip mash, and smooth the top.
- Bake at 180°C (350°F) for 20 to 30 minutes or until top is beginning to brown.
- Remove from oven, let rest a minute, then serve.