Boil the cashews, potatoes, and carrots until tender (about 8-10 minutes). Drain well and set aside.
Place macaroni in a large pot of salted boiling water. Cook until al dente and according to package directions (about 9-10 minutes). Drain and set aside.
Place all ingredients in a high-powered blender(except garlic & butter). Blend until potatoes, carrots & cashews have completely broken down and sauce is smooth, about 1-2 minutes. Set aside.
Heat up butter in a large pan over medium heat. When melted, add garlic and sauté for 30-60 seconds, until lightly golden and fragrant (be careful not to burn).
Pour in the cheese sauce and cook for 4-6 minutes until sauce thickens up and becomes slightly stretchy. Stir often to prevent burning. If it's too thick, add a splash of broth. Taste for seasoning and add more if needed.
Now add pasta and gently toss to coat. Serve immediately. Enjoy!
Notes
I usually start blending the sauce 5 minutes before the pasta will be done. This way the pasta isn't sitting too long, and it will be hot & fresh when it goes into the sauce.
To make it easier, cook potatoes, cashews and carrots the night before and pop them in the fridge.
If you'd like a thinner cheese sauce, use only 2 tablespoons of tapioca starch, or omit it altogether. The sauce will still be rich and creamy. Tapioca starch provides extra thickness and a slight "cheesy" stretch.
The cheese has a very smooth and creamy texture. So, if it comes out a bit grainy, you may need to blend longer. If it's still grainy, your blender may not be strong enough to pulverize the cashews completely smooth.
If you'd like to add another layer of flavor to the sauce, you can try ½-1 teaspoon of miso paste, apple cider vinegar or dijon mustard. Blend it up with the cheese sauce.