From Isa Moskowitz's "Veganomicon.": "Fresh cauliflower teams up with succulent mushrooms in a velvety leek and herb gravy. And what's not to love about a satisfying biscuit-style top crust flecked with savory black olives?"
Preheat the oven to 375 degrees. Use a large, oven-to-table Dutch oven. If you don't have one, use a large, heavy-bottomed pot to prepare the filling and a large, deep casserole dish to bake the finished potpie.
In a heavy-bottomed saucepan (not the Dutch oven) over medium heat, melt the margarine and sprinkle in the flour. Stir to form a thick paste. Cook the mixture until fragrant, bubbling, and lightly browned, 4 to 5 minutes.
Temporarily turn off the heat. Slowly pour in the soy milk, using a wire whisk to stir until smooth. Whisk in the dried herbs, mustard powder, salt, and bay leaf. Turn on the heat to medium and cook, stirring constantly with whisk, for 8 to 10 minutes, until a thick sauce forms. Turn off the heat, remove the bay leaf, and adjust the salt and pepper to taste.
Heat the oil in the Dutch oven over medium heat. Add the mushrooms, leeks and carrots, and saute for 6 to 8 minutes until most of the excess liquid from the mushrooms has evaporated. Add the cauliflower, stir briefly, cover partially, and steam for about 8 minutes, until the cauliflower has just begun to soften. Remove the lid, turn off the heat, and set aside.
Prepare the crust while cauliflower is cooking:
Sift together the flour, baking powder, salt and thyme in a small bowl. With a pastry cutter or two knives held together cut the cold margarine until crumbs form, then drizzle in tablespoons of cold water and mix. Drizzle in additional tablespoons of cold water, one at a time, until a soft dough forms (but careful not to overwork it). Fold in the olives.
Pat out the dough on a lightly floured surface or give it a few rolls with a rolling pin, to form a circle or appropriate shape slightly smaller than the Dutch oven. Using a sharp knife, cut the dough into diamonds (you'll be placing small squares of dough over the casserole, rather than one big disc of dough).
Give the sauce a good whisking (no worries if a skin has formed over it), pour into the cauliflower mixture, and stir completely to blend the veggie juices and sauce. Arrange the diamonds of dough over the mixture and brush with soy milk. Bake for 35 to 40 minutes, until the cauliflower is tender and the biscuits are cooked.
Allow to cool at least 10 minutes before serving, as the filling will be boiling hot straight out of the oven.