This is not the most accurate way to temper chocolate, but it is easy and a very good place to start.
Melt two-thirds of the chocolate in a bain-marie. To make the bain-marie, fill a pan one third full with water and place it over a low heat. Then place a glass or metallic bowl on top, making sure that the bottom of the bowl does not touch the water. Once the water is barely simmering add the chocolate and leave it to sit until the chocolate has completely melted.
Once the chocolate has melted, remove the bowl from the bain-marie but keep the heat on low. Place the bowl on the work surface and add the remaining one third of the chocolate to it. Stir gently until all of the chocolate has melted. Keep stirring it, and then check that it is ready by dabbing some on your inner wrist – it should feel very warm. Use the tempered chocolate as you need to, keeping in mind that the chocolate must remain at this temperature to be ‘in temper’.
If the chocolate starts to firm up around the sides of the bowl and becomes thick and hard to stir, then you know that it has come out of temper, so pop it back on the bain-marie for a moment or so now and again, not allowing it to go any higher or lower than the ‘warm wrist’ temperature.
If it becomes too cool, then you will need to temper the chocolate all over again. To do this, melt the chocolate in your bowl again. Following the same ratio of two-thirds melted to one third solid chocolate, add another third of solid chocolate to the melted chocolate and repeat the tempering process again until it reaches the correct temperature.
This method is more accurate, but you do need a sugar thermometer. Melt all of the chocolate in a bain-marie, stirring until you reach a temperature of 46–49°C (92–98°F). Then set the bowl with the melted chocolate into an ice bath (a larger bowl filled with some ice and water) and bring the temperature down to 27°C (80°F). Finally, put the bowl back on the heat and allow the melted chocolate to come back up to 31°C (88°F). The chocolate is now tempered and ready to use.
When you are tempering white chocolate with a thermometer, temperatures differ slightly. First of all you need to melt white chocolate in a bain-marie until it reaches 40–45°C (105–113°F), then you will need to bring the temperature down to 26–27°C (79–8l°F) in the ice bath. Finally, bring the temperature of the chocolate back up to 29–30°C (84–86°F) over the bain-marie. The white chocolate is now tempered and ready to use.