By hand, this means spreading it out and scraping it up, over and over, on a polished stone slab while it cools. As the desirable crystals form, it takes on a dull, claylike consistency for which the professional term is "mush." Of course there are computer-controlled machines to do this at scale.
The mush can be added back to a larger pool of melted chocolate, and as long as it's not hot enough to melt the seed crystals, this produces a pool of "tempered" chocolate that can be poured into bar molds or decorative molds, or kept warm and agitated while things are dipped in it to make filled chocolates.
White chocolate is cocoa butter with sugar and vanilla and milk powder, but without any of the actual cocoa. As long as it's made with actual cocoa butter, it shares the melting/tempering/setting properties of actual chocolate, although the thermal profiles are a little different.
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