Rhubarb & Fennel Cocktail

There is a saying if it grows together, it goes together: Sweet and sour from the rhubarb and herbaceous from the fennel, this drink is pure harmony in a glass.

• 1/4 fennel bulb, untrimmed, coarsely chopped
• 375ml no. 18 dry vermouth
• 1 large rhubarb stalk, thinly sliced, plus more, shaved, for serving
• 100ml sugar
• 150ml fresh lemon juice
• 150ml gin