If you need to cook the potato, you can microwave it or put it in a pot over the stove and cook covered for about 20 – 25 minutes. If you do this it will have more moisture and the sauce will be a touch thinner but you can cook it down at the end to get it thicker if you prefer. You can also put the cashews in to boil instead of soaking them overnight if you don't have a high speed blender.
Sauté the chopped onion and garlic with a drizzle of oil or broth until browned. About 5 minutes.
Add the white wine and cook until slightly reduced. You still want liquid, just want it to reduce a touch, about ¼ max. Should take 3-5 minutes.
Put the onion/garlic/wine mix along with the rest of the ingredients (make sure to measure out the potato) into a blender and blend on high until creamy and smooth.
You can pour into a fondue or regular pot and serve with any dippers you want. If you want the cheese thicker, cook it a bit in a regular pot on the stove over low heat.
Notes
I used red potatoes but any starchy potato will work, just don’t use sweet.
If you are not using a high speed blender you can either soak the cashews overnight or grind them into a fine powder using a coffee grinder. You can also boil them with the potato and onion.
If you have an Instant Pot, put the raw potato, onion and cashews inside with 2 cups water. Cook on manual high pressure for 5 minutes. Allow the steam to release.