All you will need is:
5 lbs russet potatoes
12 oz roasted & salted cashews
a little bit of salt to taste, about 1 tsp
Peel, and cut the russet potatoes into even chucks. Place in a large pan, and cover with cool or room temperature water. Add about 1 TBS of salt to the water to help season the potatoes. Simmer for 15-20 minutes, a fork or butter knife will insert easily into the potatoes when they are done cooking.
Place cashews into a medium saucepan, and cover with water by a couple of inches. Simmer for about 10 minutes. Blend with a stick blender until smooth. We will need to add enough water to make 4 cups total of cashew puree.
Mash the cashew puree with the potatoes. You may need to add a little salt to taste. It shouldn't need much more than a teaspoon. You will need to add more if using unsalted cashews.