What gives real white chocolate its snap-and-melt feeling on your tongue even though it contains no cocoa powder?

Answer: Cocoa-butter crystals

Sugar crystals dissolving — Sugar crystals can affect graininess, and sugar will dissolve once saliva gets involved, so this is a plausible guess. But the fast tongue-melt of chocolate is mostly a fat event: cocoa butter is solid at room temperature and melts near mouth temperature. Sugar also cannot explain a glossy snap after tempering. The bigger lesson is that chocolate texture is less about sweetness and more about how fat molecules pack.

Milk solids setting — Milk solids help with creaminess and flavor, so they are easy to over-credit. But a bar's snap comes from a solid fat crystal network, especially when cocoa butter is tempered into the desirable form. Milk solids are passengers in that fat-and-sugar matrix, not the main scaffold. This is why a dairy-rich bar can still feel waxy if the fat phase is wrong.

Cocoa-butter crystals ✓ — Right. Cocoa butter can crystallize in several forms, and tempering tries to favor the form that gives gloss, snap, and a clean melt. Sources put the desirable Form V melting point around 33 to 34 °C, just below body temperature. That tiny temperature trick lets a bar stay solid on the counter but disappear on your tongue. White chocolate lacks cocoa powder, but it still has the fat physics of chocolate.