Sour-Cherry Gin Slings

Make the gin slings: In a large saucepan, combine the cherries with the sugar, water and citrus zests and bring to a boil. Cover and simmer over low heat for 40 minutes. Pass the mixture through a fine strainer, pressing on the solids; you should have 2 1/2 cups. Let cool. Make the gin slings: In a pitcher, combine the gin with the Cointreau, lime juice, sour-cherry syrup and a few dashes of bitters and stir well. Pour into ice-filled glasses and top each drink with sparkling water. Garnish with the lime wheels and fresh cherries and serve.