The macadamia is one of the most luxurious of nuts. Large, round, sweet and extremely rich and fatty, the macadamia is also one of the most expensive, largely because the smooth, seamless shell is extremely difficult to crack, needing a reported 21kg of pressure per square centimetre. I've never seen macadamias sold in their shell in Hong Kong markets (although you can buy them online), but even if I did, I'd stay away from them; sometimes it's worth paying someone else to do the hard work. If you are up to the challenge, roasting or boiling the nut is said to make the shell easier to crack.
The macadamia is indigenous to Australia, although the country is now second to Hawaii in terms of production and export. Like all other high-fat nuts, the macadamia can quickly become rancid, especially in warmer weather, so it's best to store them, tightly wrapped, in the freezer. The nut is also made into paste (macadamia butter) and pressed into oil.
Many of us first tasted the nut as a chocolate-covered macadamia from Hawaii. Unfortunately, they were always covered with mediocre-quality milk chocolate, making for a confection that was far too sweet. Making a vastly superior version isn't difficult: all you need to do is temper some good bittersweet chocolate, pour some of it into moulds, add a couple of roasted macadamia nuts (salted ones would be good, too) then cover them with more tempered chocolate and leave until it sets.