1. Grease a 13x9" baking dish. For filling, saute onion with the garlic in large kettle pot. Add celery, pepper, and tofu. Saute until onion is translucent, and the tofu is browning.
2. Add cauliflower, broccoli, and carrot, then water and seasoning. Cover and cook over medium heat until veggies are tender. Preheat oven to 400 degrees F. Strain veggies out of broth, and add to prepared baking dish.
3. Add 1 cup milk and vegan butter to broth. Heat to a low boil, then reduce to a simmer. Sprinkle the flour or cornstarch a little a time over the surface of the liquid and whisk in quickly to avoid clumps. Heat until edges froth up and it is a little thinner than the consistency you want.
4. Pour sauce over veggies in the casserole dish and mix up a bit. For topping, mix biscuit mix, 1/2 cup milk, and egg replacer with a fork and spread over hot filling. Bake for 20-30 minutes, or until topping is golden and done.
This casserole cooks quickly in the oven because the filling is already cooked and hot. I used cauliflower instead of potatoes because potatoes don't freeze well and I like to put a batch in the freezer to make a quick dinner on weekdays. In that case, you just defrost, put some biscuit dough on top, and voila! Your own homemade frozen dinner!