Special equipment: a mandoline; a deep-frying thermometer
Slice the potatoes on a mandoline as thinly as possible. Submerge the potato slices in cold water as you go to keep them from browning. This will also remove any excess starch.
Add the dry ranch seasoning, parsley, onion powder, salt, garlic powder, dill, paprika and black pepper to a bowl and mix. Set aside.
Fill 2 large Dutch ovens halfway with vegetable oil and heat to 375 degrees F.
Drain the potato slices and lay out on baking sheets lined with paper towels. Use more paper towels to blot the slices until completely dry.
Lower batches of potato slices into the oil using a spatula and fry until golden, 1 to 1 1/2 minutes per batch. Remove with a slotted spoon to a baking sheet, immediately sprinkle over some of the seasoning mix and toss until evenly coated. Repeat with the rest of the potatoes.