Make the middle first. Heat the Dulce de Leche in a pan for 1 min until warmed and runny.
Then stir in the chopped dark chocolate and leave to melt. Stir until smooth.
Cover a dinner plate with cling film, then tip the mix onto it.
Cool, then freeze for 2 hours or until very firm.
Put the milk chocolate into a bowl.
Bring the cream to the boil in another pan, then pour it over the chocolate.
Leave for 2 minutes, then add the vanilla and stir until smooth.
Cool, then chill until set.
Peel the caramel from the cling film, then snip into thumbnail-size pieces; wet kitchen scissors work best.
Spread cocoa powder over a large baking tray.
Take a heaped tsp of the truffle mix then, with cocoa-dusted hands, poke in a caramel chunk.
Squash the mix around the caramel to seal, then roll into a ball.
Put onto the tray, then shake to coat in the cocoa.
Repeat with the rest of the mix, then freeze, or chill if making less than 3 days ahead.