Making your own chocolate treats at home is one way to control what goes into them, and it's a fascinating hobby, as well. It's the kind of thing you might do for years, and still learn something new with almost every batch. Unfortunately, one of the first things you'll learn is that it's not as easy as it looks. Any chocolate treat should taste good, but getting the chocolate to harden and form a glossy shell – the way the pros do it – takes a bit of finesse. It's not difficult as such, but it does require some patience and practice.
Manage Your Temper
Chocolate is made up largely from fat – in this case, cocoa butter – with cocoa particles, vanilla and various other ingredients suspended in it. If your homemade chocolates aren't hardening, it's because cocoa butter can be a bit weird to work with. Real butter is simple: It hardens when it's cold, and melts when it's warm. That's because milk fat is all the same kind of fat, and it behaves predictably. Cocoa butter doesn't, because it's made up of several different fats. Most of them, like real butter, are soft and squidgy at room temperature. If you want your homemade candies to be glossy and hard, like the ones pros make, you'll have to melt and cool the chocolate at very specific temperatures. This process is called "tempering" the chocolate.
Basically, tempering is a struggle for control that goes on inside the chocolate. You know that old saying about square pegs and round holes? Well, when you're working with chocolate, it's the temperature of your chocolate that determines how it hardens. The fats that solidify first, at any given temperature, set the structure for the others in your chocolate. At a temperature that's too high or low, the fats stay soft when you're done. If you get it right, they form a rigid crystal structure that makes the chocolate harden and turn glossy. Going back to the pegs and holes metaphor, you've suddenly got all squares instead of a random mixture. To get to that stage takes some patience, and it's a lot easier if you have an instant-read thermometer the first few times you do it.
Sow Some Seeds
There are several ways to temper chocolate, but the easiest for amateurs is what's called the "seeding" method. Basically, you melt the chocolate, then stir in some already-tempered chocolate that you've shaved or grated to make it melt quickly. This is basically any bar that's already hard and glossy, like the Lindt or Ghirardelli bars you'd find at the supermarket, or just keep back some of the chocolate you've started with. The shavings seed your melted chocolate with the form of fat crystals you want, and as long as your chocolate stays below the melting temperature of those crystals, you're good to go.
Here's how it works. Heat your chocolate until it's just melted, which is usually 114 to 118 degrees Fahrenheit for dark chocolate or 105 F to 113 F for milk chocolate. Now, stir in your "seed" chocolate until it's melted. Finally bring your chocolate back up to its working temperature, usually 88 F to 89 F for dark chocolate or 84 F to 86 F for milk chocolate.
To test whether you've gotten it right, spread a thin smear of chocolate on a corner of wax paper and chill it for a moment or two in the fridge. If it's glossy and snaps when you bend it, congratulations! You've just tempered some chocolate. If it's still dull and soft, that means you didn't get it quite right. Don't worry, even seasoned pros have to re-do a batch periodically. Just re-warm the chocolate and start over. It helps if your kitchen is cool and dry, so if you're in a hot and humid climate, you should probably crank up the air conditioning while you work. Once you've got it tempered, keep the chocolate warm as you work by setting it over a heating pad, or by giving it just a few seconds over a hot water bath. Don't over-warm it, or you'll put your batch out of temper and have to start again.
Fix It in an Emergency
Knowing how to do chocolate the right way is a good long-term strategy, but it doesn't help when your chocolates are already made and you're running out of time. If you've already got a tray of candies that didn't harden, cold is your friend. Even untempered chocolate will temporarily harden up in the fridge or in the freezer, depending on how much of a time crunch you're facing. Bear in mind they'll stay hard only as long as they stay cold, so it's best to bring them out right before they're served.