Take the lamb out of the fridge at least 30 minutes in advance. Season. Preheat the oven to Gas Mark 6, 200°C (400°F).
Heat the oil in a large, non-stick frying pan. Add the lamb, fat-side down and sear quickly on both sides until lightly browned. Leave until cool enough to handle.
Meanwhile, mix the breadcrumbs with the garlic and parsley. Mix the mustard with the Herbes de Provence.
Smear the racks of lamb with the mustard mixture then press the breadcrumbs on firmly so that the meat is entirely covered.
Roast for 30 minutes. The lamb with be medium at this stage. Remove from the oven. Cover with tinfoil and allow to rest for 5 minutes. Slice the racks between the bones and serve with sautéed spinach and gratin potatoes.
You can replace the parsley (all or part) with a choice of other fresh herbs: tarragon, basil, chives or sage.