For the lavender-honey syrup: Combine the sugar, honey and 2/3 cup water in a small saucepan over medium heat. Bring to a simmer, stirring to dissolve the sugar. Stir in the lavender flowers. Return to a simmer, then remove from the heat. Let cool completely, then strain and discard the flowers. (This makes enough syrup for 10 to 12 cocktails.)
For the cocktail: Combine the mint leaves and 1 tablespoon of the lavender-honey syrup in the bottom of a cocktail glass. Use a muddler or the top of a wooden spoon to muddle and press the mint to release its oils. Add the bourbon and stir. Fill the glass with copious crushed ice. Garnish with a mint and lavender sprig or two and serve immediately.