Trim/ clean any of the excess fat and sliver skin from the top rack of lamb (save the trim).
Season the rack of lamb with salt and pepper (set aside).
Render down the lamb trim with a pinch of salt in hot pan.
Then sear the rack of lamb in the pan oil. Brush the lamb with Dijon mustard.
Add all herb crust ingredients minus the sourdough in a blender and blitz. Once combined and in the sourdough chunks. Blitz until a fine crumb. Press crumb in lamb to create a herb crust.
Transfer the rack of lamb in the oven at 160 c till the probe reaches 48 degrees.