Combine 2 baskets raspberries and 2 tablespoons sugar in medium bowl. Mash berries lightly with fork. Let stand 15 minutes. Mix in liqueur and brandy. Pour into jar. Cover and let stand in dark cupboard 3 days. Strain raspberry mixture, pressing on solids with spoon to extract as much liquid as possible. (Can be made 1 month ahead. Cover; chill.)
Place 1 sugar cube in each of eight 6-ounce champagne flutes. Pour 2 tablespoons raspberry mixture over each sugar cube. Pour champagne over to fill glasses. Garnish each with raspberries and lemon peel.
