Bring a large pot of salted water to a boil. Add the potatoes and cook for 12-15 minutes until fork-tender.
Drain the potatoes well in a colander. In the same pot the potatoes were cooked in, bring fresh water to a boil.
Transfer the drained potatoes to a blender along with the tofu, nutritional yeast, olive oil, asafetida, onion, umeboshi vinegar, water, and truffle oil. Blend until completely smooth.
Add the tapioca starch and blend for an additional 20 seconds until smoothly combined.
Add the macaroni to the pot of boiling water and cook until al dente according to package directions.
Drain well and return the pasta to the pot. Pour the truffle cheese sauce over the macaroni and stir until evenly coated.
For the optional topping, combine the porcini powder, breadcrumbs, and smoked paprika in a small bowl.
Spread the mac n cheese into a casserole dish and top with the seasoned bread crumbs.
If desired, bake at 375°F (190°C) for 15-18 minutes until the topping is golden and crisp.
Serve hot, optionally garnished with chives and parsley.