Strip the leaves off one mint sprig. Lightly slap the leaves in the palm of your hand to release the oils, add to a chilled white wine glass.
Fill the glass with ice, then add in the St. Germain, chilled Prosecco and seltzer. Stir briefly to combine.
Garnish by placing a lemon wheel into the glass, alongside a bouquet of 2–3 additional mint sprigs.
