This one is a no-brainer, save for one very important detail: never (really, never) use high quality chocolate to top a doughnut. Why not? Because truly good eating chocolate deserves to be eaten on its own. Combining high quality chocolate with a high quality doughnut ruins them both, as they compete for attention (kind of like pairing a truly great wine with a truly great dinner…a waste). Use the absolute cheapest chocolate you can find. In fact, don’t even use chocolate if possible, use a “coating” chocolate, one without cocoa butter in it. Occasionally you can find it in big grocery stores. If that fails, then let your wallet decide. Trust me on this, you won’t be sorry. Just melt the chocolate in the microwave (one burst of 20 seconds on high, followed by 3-4 more 10 second bursts) until the chocolate is completely melted:
…and remove to a rack or plate to let cool and harden.