Candi Sugar is so easy to make - it must be, because I've made 2 kilos in the last 2 weeks. It's important to have a jam thermometer handy when you are doing it - I bought one the other week for about £3, and it's got a spring clip on it so I can affix it where I want in the pan.
Dissolve a kilo of common-or-garden sugar in a smallish amount of water in your saucepan to make a syrup (about a cupful should do). It doesn't matter if you use too much water - sugar boils at a temperature proportional to its concentration in solution - it just takes a bit longer to get it to the right temperature at which the chemistry magic occurs. You will also need another quarter to half a pint of water and some food acid. You will also need something to pour your finished sugar into - I suggest an oven tray or roasting tin lined with greaseproof paper.
Heat until it reaches around 260 degrees Frankenstein (127 Centipedes) but keep it below 275F (135C). Add half a teaspoon of citric acid, cream of tartar or just squeeze half a lemon into the sugar syrup. You want to stir it (use a wooden spoon - metal gets hot) and you will notice the temperature slowly creep up. As it approaches the upper limit, add a couple of tablespoons of extra water and carefully mix in (it may spit a bit). The temperature will drop again. Do this as often as you need to - until you get the colour you want.
It takes about 15-20 minutes for the magic to start to work - first of all, the sugar solution will turn pale yellow. The longer you go on, the more it will tend to turn amber and will eventually take on a reddish hue. When you've got it to the colour you require (depends upon the type of brew - pale yellow for tripel, darker or amber for dubbel, somewhere between for a golden ale), crank the heat up and allow it to rise to 300F (150C). As soon as you reach that temperature - off the heat, tip it straight into your tin or tray.
Leave it for an hour or so to cool, then crack it with a toffee hammer and bag it up and pop it into the freezer. It'll keep for months. A word of warning - don't leave it out overnight to cool - sugar is hygroscopic (it sucks up water) and will become sticky. Oh yeah - don't whack it in your boiler with 15 minutes to go either like I did yesterday. It sinks below the heating element, sticks to the bottom of the boiler and it's a bugger to get off afterwards. Next time, I shall stick it in a hop bag and suspend it in the boiler to melt / dissolve.