Wash the potatoes thoroughly. Using a mandoline or the slicing attachment of a food processor, slice the potatoes very thinly.
Place the slices in cold water and soak for 30 minutes to remove excess starch, then drain.
While the potatoes soak, make the dip: combine sour cream, mayonnaise, finely diced yellow onion, dried dill, and salt and pepper to taste in a bowl. Refrigerate until ready to serve.
Pour peanut oil into a large pot or Dutch oven to a depth of a few inches and heat over medium to medium-high until it reaches frying temperature (see note: test with one slice).
Dry the potato slices thoroughly with clean towels or paper towels. Work in batches (about 4 batches) so the oil temperature stays steady.
Fry one batch at a time, stirring occasionally for even cooking. Fry for about 3–5 minutes, or until slices are browned and crisp like chips.
Use a slotted spoon to transfer chips to paper towels to drain. Immediately sprinkle with sea salt. Repeat with remaining batches.
Serve the warm chips with the chilled sour cream-dill dip.
Test oil temperature by frying a single potato slice: it should sizzle evenly and constantly but not violently; adjust heat if necessary.