Lavender is not usually associated with culinary herbs, with the exception of Provence. French chefs in and around Provence have been incorporating this herb into their cuisine for many centuries. Lavender lends a floral, slightly sweet and elegant flavour to most dishes. For most cooking applications it is the dried buds (also referred to as flowers) of lavender that are utilised, though some chefs experiment with the leaves as well. It is the buds however that contain the essential oil of lavender, which is where both the scent and flavour of lavender are best derived. Some French chefs claim that Herbes de Provence is not authentic unless it contains lavender flowers.
If you do experiment with lavender as a culinary herb, be extremely wary of the amount that you use or you will have a dish with the scent reminiscent of a very clean toilet!