In a small saucepan over medium-high heat, bring sugar, water and lavender extract to a boil.
Once sugar is dissolved, remove from heat and chill completely before using in the cocktail.
Add rose, grapefruit juice, lavender simple syrup and egg white to a shaker filled with ice.
Shake vigorously for 10 to 15 seconds.
Pour cocktail into a coupe glass and top with champagne.
Garnish with lavender buds and serve.