On a small plate, stir together the sugar and grated lemon zest. Dip a clean finger in the lemon juice and moisten the rim of a Champagne flute or other wine glass. Dip the rim in the sugar mixture to coat.
In a small bowl or ramekin, using a cocktail muddler or the end of a wooden spoon, pulverize the raspberries with the limoncello. Transfer the puree to the sugar-rimmed glass. Place a spoonful of crushed ice in the glass, then pour in the sparkling wine. Garnish with the mint leaves or lemon zest strip and serve immediately.