Preheat the oven to 180 C (no fan).
Combine the water, Henderson’s Relish (or alternative), soy sauce, Marmite, mushroom seasoning powder, thyme, and bay leaves in a bowl and put it to the side while you prepare everything else.
Line the bottom of a casserole dish (or in my case a cast iron pan) with half of the potatoes. Spread the sliced carrots over the potato layer.
Add the wine to a large frying or saute pan and bring to a simmer. Dump the cubed tempeh in and toss with some kind of culinary implement to coat the tempeh. Continue simmering, stirring frequently, until the wine is completely absorbed and any remaining wine is a sticky glaze on the pan. Now add a tablespoon of the oil to the pan, toss to coat all the tempeh pieces, and fry on medium high heat for 5-7 minutes, until the tempeh is browned. Tip the tempeh into the potato lined casserole dish.
Turn the heat back down to medium and add the butter and remaining 1 tablespoon of oil to the same saucepan. Add the onions and fry, stirring from time to time, until they’re lightly browned and caramelised, sometime in the ballpark of 10 minutes.
Add the flour. Stir to incorporate with the onions. Pour the liquid from step 1 into pan, give it a good stir, and cook until it thickens slightly. Taste and season with salt and pepper to taste (but remember the sauce will reduce in the oven so don’t over salt). Pour the contents over the tempeh and carrots.
Cover with the remaining half of potatoes. For a crispier finish you can drizzle some more oil over top or add a few dollops of vegan butter or margarine.
Cover with a lid or foil and bake for 45 minutes. Remove the foil and and bake for a further 30-45 minutes, until the potatoes are browned to your liking.