Lay the pork belly for the chashu in a heatproof container, overlapping the slices, and add 1/2 tablespoon soy sauce and a pinch of sugar, coating it all over. Overlapping the slices keeps them from shrinking up as they cook, giving chashu with a clean cross-section.
Pork belly (for chashu) 140gSoy sauce (for chashu) 1/2 tablespoonSugar (for chashu) a pinch