Lightly toast the pine nuts and almonds. Break up the nuts in a food processor or use a pestle and mortar until the nuts are broken into slightly smaller pieces, but not too finely ground.
Put the sugar and measured water in a small heavy-based saucepan and heat very gently, stirring until the sugar dissolves. Bring to the boil and cook, without stirring, until the syrup has turned to golden caramel. This will take 6–8 minutes. Immediately dip the base of the pan in cold water to prevent further cooking (if you overcook it, the resulting praline will taste bitter) and stir in the nuts.
Work quickly as you turn the praline on to a large lightly greased baking sheet, spreading it out in a thin layer before it starts to set. Leave for about 1 hour, until the praline is brittle.
Melt the chocolate in a heatproof bowl over a pan of gently simmering water. Break the praline into pieces and place on a wire rack. Drizzle with the melted chocolate, then leave to set. The praline will keep, in an airtight container in a cool place, for up to 1 week.