2 sprigs thyme, leaves removed and stems discarded, plus more for garnish
8 ounces high-quality cognac, divided
Ice
Sparkling wine
Directions
On a sheet pan, spread half of the grapes evenly over the bottom of a pan. Place in the freezer and freeze at least 6 hours or overnight.
In a cocktail shaker, muddle the sugar, 12 to 15 of the nonfrozen grapes, lemon juice and three-quarters of the thyme leaves. Add the cognac and ice and shake. Fill each of 4 Champagne flutes with 5 to 6 frozen grapes and strain equal parts of the cognac mixture into each glass. Top with the sparkling wine and garnish with a sprig of thyme.