Heat some oil to 350°F in a deep pot for later. Boil both the sweet potatoes and russet potatoes in salted water until very soft. Mash them separately with a potato masher, stir in the butter and egg yolks, season with salt, pepper, and nutmeg, and refrigerate both sets of mashed potatoes until cold.
Fry the bacon slices on both sides and set aside.
Divide the mashed sweet potatoes into 4 portions. Take 1 tbsp of shredded cheese, shape it into a smooth ball, place it in the middle of one sweet potato mash portion, and roll that into a smooth ball. Repeat with the other 3 portions of cheese and mashed sweet potatoes.
Wrap 2 slices of bacon around each ball and lightly squeeze to hold them in place.
Divide the regular mashed potatoes into 4 portions. Put a piece of plastic wrap on a cutting board and press a mashed potato portion flat on it. Place the bacon sweet potato ball in the middle and shape the mashed potato mixture into a sealed ball. Repeat with the rest of the portions.
Whisk the egg and crush the potato chips. Then roll each bacon potato ball in flour, egg, and chip crumbs.
Fry the breaded potato balls in oil heated to 350°F for 5-7 minutes.
