Cut the rhubarb into small pieces.
Make the sugar into caramel in a large saucepan, extinguish with the water and let it boil.
Add the rhubarb and lemon zest. Make closed at low temperature for 40 min, stirring occasionally.
Spread a sieve with a wet straining cloth and pour the gravy through. Now refrigerate.
For the cocktail, pour 1 centiliter of apricot brandy in a glass form and top up with the rhubarb juice and sparkling wine.