In a medium-large pot, heat water for pasta. Add 3 teaspoons (or 1 Tablespoon) of the salt to water. Once boiling, add pasta and cook according to package. Strain and put pasta back into the same pot.
Meanwhile, fill a medium pot with water and potatoes, bring to a boil, and cook until potatoes are soft (~ 10-15 mins). Strain potatoes and set aside.
Carefully add potatoes to the blender/Vitamix container, along with the rest of the ingredients (including the remaining 2 t of salt). Puree altogether.
Now pour your "cheese" over the pasta and mix together.
Video
Notes
To serve...scoop mac & cheese into bowls or plates. Serve alone or with a side, like a mixed greens salad.
To make this nut-free...use carrots or flour as a thickening base, instead of cashews. If you're gluten-free, use a wheat-free pasta, like Banza chickpea-based pasta. And, FYI, nutritional yeast is gluten-free.
Because of their fun shape, we love shells. But other excellent pasta options are: macaroni (obvs!), rotelle (wheels), farfalle (bowtie) or cavatappi (corkscrews).