Melt (decrystallize) as much chocolate as you need in a heatproof bowl. When it is completely fluid, and has no lumps in it. Check the temperature of the melted chocolate, it should be 55-58°C for dark chocolate, 45-50°C for milk chocolate and white chocolate.
Then pour three-quarters of it on to a cool, dry slab of marble. When I say cool this means not warmed by any bowls of chocolate, but not to be artificially cool, as this will cause the chocolate to crystallize too quickly. If that happens it will bloom and be difficult to work. Scrape chocolate remaining in the bowl down the sides so it doesn’t cool too quickly.
Now, with the help of a paddle/scraper (the sort of large triangular blade used for DIY to fill holes with plaster), spread the chocolate over the marble. This will cool down the mass of chocolate and start to encourage the formation of the crystalline structure.
Then, holding the paddle in one hand and the palette knife in the other, quickly regroup the chocolate into the centre of the marble, being careful not to leave any trails behind, as they will cool too quickly. We are aiming to keep the temperature uniform as it cools. Repeat steps 3 and 4 a few times – notice how the chocolate begins to thicken.
Use the digital thermometer to check the temperature, but don’t hang about as the chocolate is cooling all the time. When the dark chocolate has dropped to 28–29°C (milk chocolate 26–28°C, white chocolate 26–27°C) it is tempered and ready for the remaining melted chocolate to be added. (Be careful that it does not get too cool, you may be able to gently warm it but you might have to start all over again!) Many professional chocolatiers test the temperature by dipping their finger into the chocolate and then touching their bottom lip, as it is time-consuming checking the thermometer all the time, and, in fact, the lip is a very accurate gauge of temperature once you know what you are doing.
Now add the remaining melted chocolate. This will bring up the temperature by about 2°C, which is the final stage of the ‘tempering curve’ (melting, cooling, then raising the temperature slightly). Perfectly tempered chocolate has a very fine ‘satin’ sheen; if it has a dull finish, this is a sign that the chocolate has cooled too much and is not perfectly tempered.
Now the chocolate is ready to mould or dip truffles in. You need to be quite quick as the chocolate will lose its temper if it warms up or cools down. Transfer the tempered chocolate to a heatproof bowl. You can place the bowl of tempered chocolate in a bain-marie of lukewarm water (baby’s bath temperature), which will help to keep it workable for longer.
Keep practising – after about 10 attempts you should be pretty good!