Roast the cloves of garlic in the oven on 400° for 20 minutes in a drizzle of oil.
While the garlic is roasting, boil the cashews for 15 minutes and cook the pasta according to the package directions. Cook the frozen peas, if using.
After the garlic is done roasting, add the cashews, water, nutritional yeast, miso paste, ground mustard, salt, lemon juice, sundried tomatoes, and spinach to your blender. Start with 2 tbsp of the non-dairy milk. Blend the ingredients until smooth and creamy (you will likely need to scrape down the sides as you go.
Add more non-dairy milk 1 tbsp at a time as needed until you reach a very creamy consistency that also flows a bit. You can also adjust to your preferences by adding more or less non-dairy milk.
Once blended, combine the sauce, pasta, and peas together and mix. Serve hot. The mac n cheese can be stored well covered in the fridge for 3 to 5 days.