Preheat oven to 425°. Pat lamb dry with paper towels, then rub with 2 tbsp. or so of oil. Season all over with salt and pepper, then coat meaty sides lavishly with lavender buds, pressing them in.
Heat 1/4 cup oil in a large frying pan (not nonstick) over medium-high heat. Sear lamb on all sides, one rack at a time and pressing into pan to help lavender stay on, about 2 minutes per side. Use more oil if you need to.
Put all racks into pan, meat side up, and roast until an instant-read thermometer inserted in thickest part registers 140° (for medium rare), 15 to 20 minutes.
Move racks to a cutting board, tent with foil, and let rest 5 to 10 minutes. Slice into chops. Arrange on a platter and finish with a generous sprinkle of salt and pepper.