Lay the clean, drained berries in a single layer on a cookie sheet and place in the freezer until frozen through. It is best to do both this and the next step the day or night before you plan to make the sorbet - just make sure you leave enough time for everything to freeze.
Make the herb-infused simple syrup by combining the water and sugar in a small heavy-bottomed saucepot and heat over a medium flame until it comes to a boil. Turn it off and let cool completely.
Strain out the mint leaves and lavender and pour the cooled syrup into an ice cube tray - should make roughly 4 syrup cubes. Place the tray in the freezer until syrup is frozen (the cubes may remain a little mushy as a result of all the sugar.)
Once the berries and herb-infused syrup cubes have frozen, you can make the sorbet. Place the frozen berries and syrup cubes in the bowl of a cuisinart or blender and add a few teaspoons of ice water to aid in blending. Continue to process or blend, adding small amounts of the ice water as needed, until smooth.
Serve, topped with a sprig of mint leaves and/or lavender.