Place 2.5 cups of water and 2 cups of pasta, along with the vegan butter in your Instant Pot. Place the trivet on top of the pasta and water.
In a smaller pot (small enough to fit inside your IP), place the carrots and cashews, and add 1/2 cup of water. Cover with foil, and place inside the pot, on top of the trivet.
Place the lid on, ensuring it's sealed, and set the pot on the manual setting for 4 minutes. After the cycle is complete, release the pressure manually and remove the lid. Remove the carrot/cashew mixture from the pot and place it in a blender. Remove the trivet, and stir the pasta well.
To the carrot mixture in the blender, add the rest of the ingredients. Blend well until smooth.
Pour the cheese sauce mixture back into the pot, and add the vegan cheese. Stir well. Turn the sauté feature on for a few minutes, stirring often, just to activate the flours and thicken the sauce and allow the cheese shreds to melt.
Serve immediately.