- With your hands, squeeze the grated cucumber over a fine sieve into a bowl or jug. Add the lemon juice and the bruised mint leaves and leave to infuse for 1 hour.
- Add the elderflower cordial and chill. Wrap the remaining mint leaves in damp kitchen paper and chill.
- Place 8 champagne flutes in the freezer 20 minutes before serving. Meanwhile, shred the reserved mint leaves. To serve, divide the cordial mixture among the glasses, then top up with chilled champagne and garnish with the shredded mint.