Melt shortening in a medium skillet over medium heat. Add onions and garlic and cook, stirring, until completely softened but not browned, about 4 minutes. Add paprika, garlic powder, and tomato paste, and mustard. Cook, stirring, until fragrant and mixture starts to sizzle, about 1 minute.
Add potatoes and cashews and cook, stirring, until cashews are lightly toasted, about 2 minutes. Add water, miso paste, and milk. Bring to a boil, reduce to a bare simmer, and cook, stirring frequently, until potatoes are fully tender, about 10 minutes.
Transfer mixture to the jar of a high-powered blender. Add hot sauce and a pinch of salt. Start on low speed and slowly increase speed to high. Blend on high speed until completely smooth, about 2 minutes, adding water a few drops at a time as necessary to thin to desired consistency. Season to taste with more salt.
In a large pot, cover macaroni with cold water by 2 inches. Season heavily with salt. Bring to a boil over high heat, stirring, and cook, stirring occasionally, until macaroni is just tender (timing will vary by brand). Drain macaroni, reserving half cup of cooking liquid. Return macaroni to pot. Add sauce, set over high heat, and cook, stirring, until macaroni is evenly coated with sauce, about 1 minute, adding extra cooking liquid as necessary to achieve a creamy consistency. Serve immediately.