잡채 — Korean sweet-potato glass-noodle stir-fry, tossed in a soy-sesame sauce with vegetables and beef. Traditionally thin-sliced beef; this is the home version with ground beef.
Whisk the soy sauce, sugar, sesame oil, garlic, and a few grinds of pepper into a sauce. Pour about a third of it over the ground beef and leave it to marinate while you prep everything else.
Bring a pot of water to a boil. Blanch the spinach 20 seconds, lift it out, and run under cold water. Squeeze it bone-dry, then loosen the clump and toss with a small splash of the sauce.
Keep that water boiling for the noodles. Cook the dangmyeon 6–7 minutes until fully tender and translucent — undercooked noodles stay gummy and won't drink the sauce. Drain, and snip a few times with scissors so they're manageable.
While the noodles cook, stir-fry the vegetables in a hot oiled pan in quick batches, seasoning each lightly with salt: onion, then carrot, then pepper, then mushrooms. Keep them crisp-tender and set aside. Cook the marinated beef last in the same pan until browned.
Return the drained noodles to the warm pot off the heat, pour in the rest of the sauce, and toss until every strand is glossy and evenly colored. Toss the noodles in the sauce while they're still hot — that's when they absorb it; cold noodles just sit in a puddle.
Add all the vegetables, spinach, and beef back to the noodles. Fold everything together gently, taste, and adjust with a little more soy or sesame oil. Finish with scallions and sesame seeds. Serve warm or at room temperature.