Place gelatin leaves in a large bowl and cover with water for approx.10 min. Meanwhile, mix together vodka and elderflower cordial in a small liquid measuring cup. Drain water after approx. 10 min. and squeeze any excess water out of gelatin leaves.
Melt soaked gelatin leaves in a heatproof bowl set over a pot of simmering water. Once gelatin leaves are completely melted, add cocktail mixture and stir for approx. 2 min. Ensure, gelatin and cocktail mixture are fully combined before taking off heat and pouring into large liquid measuring cup. Add Champagne and lightly stir in to preserve effervescence.
Pour mixture into glasses and place in fridge. Remove after approx. 6 hrs. or when set and garnish with piece of lemon peel. Enjoy!