Bring a large pot of water to a rolling boil and salt it generously, like pasta water.
Blanch the spinach 30-45 seconds, pushing it under with tongs, until it collapses and turns a darker, glossier green.
Lift it straight into a bowl of ice water to stop the cooking and lock in the color.
Working in two or three fistfuls, squeeze the spinach hard and repeatedly until no more water drips out when you stop.
Loosen the squeezed block apart with your fingers so it isn't one dense clump.
Add garlic, sesame oil, soy sauce or salt, and half the sesame seeds, then massage gently with your hands until every strand is coated.
Taste and adjust salt, then finish with the remaining sesame seeds.
