Crush the lavender. Using a mortar and pestle crush the lavender into fine pieces. (If you don't have a mortar, place lavender in a bag and crush it with a rolling pin). Dump the crushed lavender buds onto a cutting board and finely mince any remaining large pieces.
Marinate the chicken. Put the crushed lavender into a large bowl along with the olive oil, lemon juice, lemon zest, honey, fresh thyme, salt, and black pepper. Whisk together until combined. Pat the chicken thighs dry with a paper towel and add them to the bowl. Toss well to coat in the marinade. Cover and leave to marinade for 2 hours or up to four hours (in the refrigerator).
Roast chicken. When ready to roast, preheat the oven to 400°F. Place the chicken pieces in a baking dish in a single layer, skin side up. Pour the remaining marinade over the top. Roast for 20 minutes.
Baste the chicken and continue to roast. Remove the baking dish from the oven, and baste the chicken pieces with the pan juices. Roast again for 10 minutes, then remove the chicken from the oven basting once more. Cook the chicken for 5 minutes (35 minutes total roasting time, or until the chicken is fully cooked and the internal temperature registers 175°F). Turn on the top oven broiler and broil for 2 minutes to crisp up the skin. Watch the chicken carefully to avoid over-browning.
Make the glaze. Remove the chicken from the oven and carefully transfer the pieces to a plate. Pour the leftover juices into a small saucepan. On medium heat bring the sauce to a simmer. Then reduce to medium-low heat while whisking continuously until thick, about 8-10 minutes.
Brush the glaze on top of the chicken thighs. Using a pastry brush, coat the tops of the chicken thighs with the glaze. Transfer the pieces to a serving platter and serve immediately.