For lavender sugar, fill layer a tablespoon of dried lavender buds (food grade) and pure cane sugar. Shake to release lavender oils and let sit for at least 24 hours. Sift out buds before using.
Make simple syrup: In a small saucepan, heat water and lavender sugar, stirring until sugar is dissolved. Remove from heat and let cool. Stir in lavender extract. Pour into a glass jar and chill until ready to use.
In a shaker filled with ice, combine gin, lemon juice, and simple syrup. Shake to combine. Strain into a glass and top with champagne. Garnish with a lemon twist.