Finely chop the white chocolate and place in a heatproof bowl.
340 g white chocolate
In a small saucepan, heat the cream over a gentle heat until almost boiling. Remove from heat.
190 ml double cream
Pour the cream over the chopped white chocolate and leave to sit for 5 minutes. With a spatula, gently stir the chocolate into the cream until it has completely melted and the mixture is smooth.
Add the nutmeg, vanilla (if using) and salt and very gently stir to combine.
2 ½ teaspoons nutmeg, 1 pinch vanilla powder, 1 pinch salt
Leave to cool and then place in the fridge to set for at least an hour, or overnight.
Remove the truffle mixture from the fridge 30 minutes before you are ready to roll your truffles, Take teaspoonfuls of the mixture and roll it between your hands to form a ball. It's easiest to roll the truffles if you wipe your hands clean after every few. Place onto a lined baking sheet and return to the fridge to harden again.
Finely chop the dark chocolate and place in a small bowl. Place the bowl over a pan of simmering water (make sure the water does not touch the bowl) and allow to melt, stirring occasionally. Remove from heat.
200 g dark chocolate
Using a fork, dip each truffle into the chocolate until fully coated. Make sure the chocolate isn't too warm at this point as you don't want to melt the truffles! You might have to warm the chocolate up again if it starts to get too viscous. Once coated, place each truffle onto a baking sheet lined with parchment paper and allow to set. You can place them in the fridge to set if you like.
Melt the remaining white chocolate. I find it easiest to pour this into a small freezer bag and snip off the corner - this makes a nifty little piping bag. Drizzle the tops of the truffles with white chocolate and leave to set.
50 g white chocolate to decorate
Decorate with sprinkles, if using.
sprinkles to decorate