In a large pot, bring the water and salt to a boil. Add macaroni and cook until al dente. In a colander, drain pasta and rinse with cold water. Set aside.
In a saucepan, add shallots, potatoes, carrots, onion, and water, and bring to a boil. Cover the pan and simmer for 15 minutes, or until vegetables are very soft.
In a blender, process the cashews, salt, garlic, 1/3 cup margarine, mustard, lemon juice, black pepper, and cayenne. Add softened vegetables and cooking water to the blender and process until perfectly smooth.
In a food processor, make breadcrumbs by pulverizing the bread and 2 tablespoons margarine to a medium-fine texture. Set aside.
In a large bowl, toss the cooked pasta and blended cheese sauce until completely coated. Spread mixture into a 9 x 13 casserole dish, sprinkle with prepared breadcrumbs, and dust with paprika.
Bake at 350 for 30 minutes or until the cheese sauce is bubbling and the top has turned golden brown.