Scrub the potatoes clean, then coarsely grate (skin and all). Peel and finely slice the onion (if using). Place in the middle of a clean tea towel and wring out the liquid, then transfer to a large bowl. Add the flour and crack in the eggs, season with sea salt and black pepper, then mix well to combine. Place a large frying pan on a medium heat with enough oil to cover the bottom of the pan. Shape small handfuls of the potato mixture (roughly the same size as a golf balls) into latkes, flattening gently, then carefully add to the pan – you may need to work in batches. Fry for 1½ to 2 minutes on each side, or until golden and crisp, then drain on kitchen paper. Pick the herbs and scatter into the pan with the remaining oil. Fry for a few seconds until crisp, then remove to the kitchen paper before sprinkling over the hot latkes.