In a large bowl, mix the salt into the warm water until dissolved.
Cut the potatoes lengthwise into 1/2 inch (1.25 cm) thick strips. Cut each slice into 1/4 inch (6 mm) thick fries.
Place the fries into the salted water and allow to soak for 15 minutes.
Line a large baking sheet with towels and set aside. Fill a deep pot with about 3 inches (7.5 cm) of peanut oil. Heat to 375˚F (190˚C).
Remove the cut potatoes from the water and thoroughly pat dry. Add the fries to the heated oil in batches, being careful not to overcrowd. Cook just until starting to brown, about 3 minutes.
Transfer using a slotted spoon or tongs to the towel-lined baking sheet. Repeat with remaining fries.
Once all the fries have been cooked, return the oil to 375˚F (190˚C). Add the first set of cooked fries and fry until golden and crisp, 1-2 minutes. Remove to towel-lined baking sheet. Repeat with remaining fries.
Serve immediately with salt, vinegar, and Old Bay Seasoning (optional).