Let sherbet soften only slightly before spooning into food processor work bowl. Pulse processor on/off continuously until sherbet is smooth and fluffy but not liquefied. Transfer to 2 1/2 quart chilled bowl. Stir in champagne, whisking it to dissolve any sherbet lumps. Serve immediately in chilled flutes or goblets. Garnish with lemon slices. This is the ultimate liquid refreshment, prefect on a sunny afternoon or as an opener for brunch or lunch. It's also ideal as a light summer dessert after a rich summer dinner.