Preheat the oven to 450℉ and line a baking sheet with parchment paper.
In a bowl, combine the tarragon, thyme, rosemary, Dijon mustard, garlic, and 2 tablespoons olive oil and stir until well combined. Set aside.
Place the two racks of lamb on the prepared baking sheet, fat side up (ribs curved downward). Season the racks of lamb all over with salt and pepper.
Evenly divide the herb mixture amongst both racks of lamb. Using a pastry brush or back of a spoon, evenly spread the herb mixture on the fat side of the lamb until well coated.
In a small bowl, combine the breadcrumbs and remaining 1 tablespoon olive oil. Stir to combine. Sprinkle the breadcrumbs evenly over the fat-side of the lamb. Using your fingertips, press the panko into the meaty part of the lamb.
Transfer the lamb to the oven and roast for 10 minutes. Reduce the heat to 300℉ (with the lamb remaining inside the oven) and cook until the lamb registers 130℉ for medium-rare, 10 to 15 minutes more, depending on how thick your lamb is and how you like yours cooked.
Remove from the oven and loosely cover with aluminum foil. Allow to rest for 10 minutes.
Carefully carve the lamb into individual chops. Garnish with thyme and a sprinkle of flaky salt, if using. Serve and enjoy!