In a medium saucepan of boiling water, cook the udon noodles until they are almost al dente, about 4 minutes. Drain thoroughly and transfer the udon noodles to a medium bowl. Gently toss the udon noodles with vegetable oil to keep them from sticking together.

Using a pair of sturdy metal tongs, hold the nori over an open flame and toast about 4 inches from the heat until the nori is darkened and crisp, about 5 seconds per side. Let cool, then crumble and transfer the nori to a spice grinder. Add the salt and grind to a powder.

Take 4 udon strands and carefully tie them in a loose knot near the end. Repeat with the remaining udon. In a large skillet, heat 1/4 inch of vegetable oil until shimmering. Fry 4 of the udon bundles at a time over moderately high heat, spreading the udon out in a fan, until golden and crisp, about 1 minute per side. Transfer the udon bundles to paper towels to drain, then dust with the nori salt and serve.