Mango Mint Sparklers

1/4 cup packed fresh mint leaves
1 tablespoon fresh lime juice
3 cups (24 fl oz) pure mango nectar, chilled
1 (750-ml) bottle Moscato d'Asti sparkling wine or sparkling water, chilled
Garnish: cucumber spears and fresh mint leaves

Crush mint leaves with lime juice in a bowl with a pestle or wooden spoon until bruised and beginning to break up. Stir in mango nectar, then chill, covered, at least 1 hour.
Pour mango mixture through a sieve into a large glass measure, discarding solids, then pour about 1/2 cup mango mixture into each of 6 (10-ounce) glasses and top off with Moscato d'Asti (or sparkling water).
Cooks' note:
Mango mixture can be chilled, covered, up to 1 day.

Serves 6.