• Fill a large wine glass with ice.
• Pour the elderflower liqueur and homemade lavender syrup over the ice, stirring gently to combine.
• Top the mixture with the Prosecco and club soda.
• Stir once from the bottom up to mix the layers without losing the carbonation, then garnish with a lemon wheel and a sprig of fresh lavender.

Lavender Syrup

• Combine the water, sugar, lavender buds, and butterfly pea flowers, if using, in a small saucepan.
• Bring the mixture to a gentle boil over medium heat, stirring until the sugar is fully dissolved.
• Remove the saucepan from the heat, cover it with a lid, and let the mixture steep for 15 to 20 minutes to infuse the flavors and color.
• Pour the syrup through a fine-mesh strainer into a clean jar to remove the botanicals, then let it cool completely before use.