Beat the egg whites with the salt until stiff. Add half the sugar and continue beating until the egg whites turn glossy. Mix the prosecco with the cornflour in a small bowl, add to the rest of the mixture, beat briefly. Spoon the mixture immediately into a piping bag with a smooth nozzle (approx. 8 mm in diameter). Pipe out sufficiently well-spaced mounds each approx. 3 cm in diameter onto an oven tray lined with baking paper.
Cook for approx. 65 mins. in the lower half of an oven preheated to 100°C, using a wooden spoon to keep the oven door slightly open. Remove from the oven, transfer to a cooling rack with the baking paper and leave to cool.
Put the glaze and hundreds & thousands each into a small bowl. Dip the meringues up to half way into the glaze, allow the excess to drip off, then dip into the hundreds & thousands, allow to dry.