Bring to a low simmer over medium low heat, stirring constantly until the honey dissolves into the liquid. Add the thyme leaves and set aside to steep for 30 minutes.
Strain the simple syrup, through a mesh strainer to catch any thyme leaves or detritus. Cover and refrigerate the honey syrup until cold.
FOR EACH GRAPEFRUIT MIMOSA:
Add the honey-thyme simple syrup to a coupe glass (or champagne flute.
Add the pink grapefruit juice and stir to combine. Top with chilled champagne.
Garnish with fresh thyme stem and a thin wedge of grapefruit. Serve.
Notes
I used 1 tablespoon of the simple syrup, but if you prefer a sweeter cocktail, add two tablespoons.