In a medium sized sauce pan, bring the blackberries, syrup, and vodka to a boil. Use the back of a sturdy spoon to gently mash/stir the berries. Continue cooking, stirring occasionally, for about five minutes or until the berries have fully cooked down.
Stir in the lavender flowers, and continue cooking/stirring for an additional minute. Remove the skillet from heat and let cool completely. Transfer the mixture to a sealed container and refrigerate for at least an hour, up to 2 days/
Add one tablespoon of the blackberry lavender syrup to each champagne flute. Add a small sprig of lavender, if desired, to each as well. Pouring against the side of a tilted flute, to reduce foaming, fill each glass with chilled champagne.
Serve immediately.