Preheat oven to 180C/365F/Gas 4.
For the meringues, beat the egg whites in a bowl until stiff peaks form when the whisk is removed.
Add the sugar, one tablespoon at a time, whisking well.
Add the chocolate, cocoa powder, vinegar and nuts and gently fold into the meringue mixture.
Line a baking tray with greaseproof paper and spoon small mounds of meringue mixture onto it.
Transfer the tray to the oven and turn down the heat to 150C/300F/Gas 2 immediately and bake for 45-50 minutes. (The meringues should be crisp on the outside and chewy in the middle.)
For the filling, place the cream, vanilla seeds and sugar into a clean bowl and mix together well.
For the sauce, place the chocolate hazelnut spread, butter, double cream and hazelnut liqueur into a pan over a low heat. Allow the ingredients to melt, stirring occasionally, until combined.
To serve, place a dollop of filling mixture between two meringues. Place onto a plate and pour the sauce over the top. Repeat with the remaining meringues and serve.
