Preheat the oven to 100°C and line two trays with parchment.
Whisk egg whites to soft peaks, add sugar until stiff, and fold in hazelnuts.
Pipe 18 spirals of 7.5cm diameter onto the prepared trays using a piping bag.
Bake for 20 minutes, then leave in the turned-off oven for 2 hours to cool.
Melt and caramelize caster sugar in a pan until golden-brown.
Stir hazelnuts into the caramel to coat them thoroughly.
Pour onto a greased tray, let cool until set, then break into small pieces.
Whisk cream to soft peaks and fold in vanilla, coffee, icing sugar, and praline.
Heat cream, sugar, and butter in a pan, then whisk in syrup and treacle.
Stack three meringue discs per plate, layering with cream and sauce, and garnish with praline.