Start by placing half the white chocolate in a heatproof bowl over a pan of simmering water. Once melted, take the bowl off the heat and add the rest of the white chocolate and the food colouring, if using (just use a tiny amount as the gel colours are quite strong). Stir occasionally to allow the chocolate to melt in the residual heat. Sprinkle a pinch of meringue into 10 of the holes of your chocolate mould. Once the chocolate has melted, use half to coat the insides of the holes where you have sprinkled meringue. Use the end of a teaspoon to spread the chocolate up the sides of the moulds so that the the inside is coated. Leave to set for 45 mins-1 hr.
Meanwhile, melt the other chocolates in separate bowls using the same method, then use each to coat a further 10 holes of the mould. Keep back half of each chocolate mixture, as you will need this to seal the truffles.
While the chocolate sets, make the fillings. For the Pisco sour filling, beat the softened butter together with the icing sugar until pale and smooth. Add the Pisco, Angostura Bitters and lime zest and stir well. Transfer to a piping bag and store in a cool place until needed.
To make the espresso Martini filling, melt the dark chocolate and butter in a bowl set over a pan of simmering water (or in the microwave). Remove from the heat and mix in the double cream, vodka and Kahlúa. Leave to cool for 5 mins. Transfer to a piping bag and store in a cool place until needed.
For the Cosmopolitan filling, Put the dried cranberries in a bowl with the orange liqueur and leave to soak for 15 mins. Beat the butter with the icing sugar, then stir in the cranberries and liqueur, bit by bit. Mix in the lime zest and cranberry jelly. Transfer to a piping bag and store in a cool place until needed.
Once all the chocolate has set in the moulds, pipe the Pisco sour filling into the green/white chocolate shells, the Espresso Martini filling into the espresso chocolate shells (saving a bit for sticking the beans on later) and the Cosmopolitan filling into the dark chocolate shells. Leave 2mm of space at the top of each one.
Bring the pan(s) of water back to simmering, then set the reserved bowls of chocolate over to melt them again if they have set. Use this remaining chocolate to fill up the moulds and seal in the filling. Try to fill the moulds level or just under – if they go over, they won’t sit flat when the chocolates are turned out.
Leave your truffles somewhere cool to set completely for at least 2 hrs (ideally overnight). If you put them in the fridge they will set more quickly, but they will lose their shine.
Once set completely, pop the chocolates out of the moulds carefully. Add a brush stroke of gold to the Cosmopolitan truffles using your brush pen. Stick a chocolate- coated coffee bean on each of the Espresso Martini truffles using a bit of the filling. Arrange in a box lined with baking parchment and tissue paper. Will keep in a cool place for up to 1 week.