Lavender is one of the prettiest spices; even when the plant is dried, the colour remains, although it's not nearly as vivid as when the flowers are fresh. The flavour and scent of the leaves and flowers are distinctive, pervasive and powerful. This is good if you're using lavender for aromatherapy - it's said to relax the mind, reduce stress, cure insomnia and soothe skin problems. But for almost everything else - including as a scent or to flavour food - it should be used sparingly. If you're cooking with lavender, make sure the flowers haven't been sprayed with pesticide; buy it from tea shops that sell loose tea leaves, flowers and herbs.
Lavender is grown in Provence, so it's little surprise that it's often used in the cuisine of southeast France. It's usually one of the ingredients in the herbes de Provence dried spice blend, which can also include oregano, thyme, savory and tarragon. This can be mixed with olive oil and rubbed over chicken before roasting, added to the poaching liquid for fish, or mixed into ratatouille.
Because of its calming qualities, lavender is often mixed with other dried ingredients and used to make a tisane. At the famous French tea emporium, Mariage Frères, it's used in several blends: mixed, for example, with green tea leaves, berries and rose petals, or verbena, camomile, orange zest and cornflowers; while Earl Grey gets a Provencal touch with the addition of wild lavender flowers.