Make plum syrup by pitting and cooking down plums, then allowing the mixture to drain overnight through a cheesecloth-lined colander.

The next day combine equal measures of juice and sugar over low heat until sugar is dissolved. Then cool.

Make the cocktail by putting first three ingredients in cocktail shaker with ice and shaking. Strain into glass and top with Champagne. Garnish with lemon twist and sprig of thyme.