From Food&Wine, a cocktail recipe to help get rid of some of those leftover fennel fronds (http://www.foodandwine.com/recipes/campari-fennel-aperitif). I've modified it to sub out sparkling wine for Lillet Blanc (or dry vermouth) and soda water.

Handful of fennel fronds, plus 1 small sprig for garnish
3 lemon wheels plus juice of half a lemon
1.5 ounces Lillet Blanc
1.5 ounce Campari

In a cocktail shaker, combine the fennel fronds with the lemon wheels, Lillet blanc, Campari and lemon juice. Muddle well, 20-30 times.

Add ice and shake well.

Using a fine wire mesh, strain into an ice-filled lowball glass.

Squeeze the lemon peel over the drink and add it to the glass. Garnish with the fennel sprig and serve.