Grind the coriander seeds, rosemary, garlic, and some of the breadcrumbs.
Transfer to a mixing bowl, add the mustard, olive oil, salt, and more breadcrumbs if needed.
Mix into a viscous paste. Salt and pepper the rack of lamb, then smear the mustard paste all over.
Put on a sheet tray and into a 400º oven, fat side up for 20 min or until 130º at the center.
Wrap the potato in foil and place in the oven as well - cook until a knife pierces it without resistance (30- 45 min).
Reduce the veal stock until nappe (when a spoon dragged along the bottom of the pan leaves a long slowly receding streak in its wake). Set aside.
Peel and cube the celery root and saute in the frying pan with grapeseed oil over medium-high heat until fragrant and color just begins to form.
Remove the potato from the oven; slice in half and scoop out the insides. Add to the pan with some of the veal stock (unreduced) and bring to a simmer.
Use the immersion blender to create a smooth product, add 1/2 sick of butter and cream to taste - then work the whole mixture through the fine sieve, pushing it through with a ladle.
Serve the “potato” on the plate, with the lamb chops bones crisscrossed (2-3) chops. Drizzle the dressing over the lamb and the reduction over the potatoes.
