1.Place one sugar cube in each hole ice-cube trays; stain each cube with two drops of bitters.
2.Strain lychees in syrup over a bowl, reserve syrup; quarter lychees. Divide lychees and raspberries into ice-cube trays.
3.Combine reserved lychee syrup and water; pour into trays. Freeze for 4 hours.
4.Unmould ice cubes into a chilled bowl. To serve, place two ice cubes into each cocktail glass, top with 1 tsp brandy each; pour in chilled prosecco. Serve immediately.