Cook your pasta of choice according to package directions. (Reserve 1 3/4 cups of the cooking water.)
While your pasta is cooking, peel and dice an onion, seed and dice the red bell pepper, and mince 3 cloves of garlic. Then saute them over low heat in 3 tablespoons of oil with a sprinkle of salt until the onions turn translucent.
Cut open the package of silken tofu and drain off any excess water, then add the tofu to the blender. (There is no need to press silken tofu.) Then add the sauteed onion, pepper, garlic, nutritional yeast, lemon juice, mustard, salt, and pepper.
Add 1 cup of the starchy pasta water to the blender and blend until smooth. Add an additional 3/4 cup of the pasta water and blend again until very smooth.
Put the cooked, drained pasta into the frying pan used to saute the onions and pour the tofu mac & cheese sauce over the macaroni.
Mix well and warm over low heat.
Add salt and pepper to taste, and serve hot.
Notes
Saute the onion, pepper, and garlic over low heat to bring out the sweetness of the onion and to ensure you don't burn them.
The sauce will thicken slightly as it cools, so you want it to be fairly thin when it's hot.