Drizzle the lamb racks with olive oil and sprinkle generously with sea salt, black pepper,rosemary and thyme.
Sear all over in a hot pan for 4 - 5 minutes over high heat with a little extra oil. Transfer lamb to a foil lined tray and set aside.
To make the crumb - Put the pistachios, bread crumb, garlic, butter, oil, salt and pepper into a blender and blend until combined.
Spread mustard on the larger side of each rack of lamb. pat on the pistachio mixture to the crumb. Bake in the preheated oven until the crust is golden and lamb is pink in the center, 20 to 25 minutes.
Roast for 25 minutes, until the crust is crisp. Remove from the oven and leave the lamb to rest for 10 minutes.