Lamb shanks with roasted garlic sauce

For the lamb

• 4 whole lamb shanks (maybe get an extra one in case you get a small one)
• 2 heads of garlic
• 1 lemon
• butter
• olive oil
• salt
• pepper
• mustard powder (very optional)
• cayenne pepper (or any other dried chili powder)

For the celeriac purée à la Raymond Blanc

• 1 big celery root, or two smaller ones
• butter
• milk
• salt
• cayenne pepper (or any other dried chili powder)
• lemon (you can use the same one you use for the lamb sauce)

1. Also get a green vegetable if you're into that — I did two bunches of broccolini
2. Put the shanks in a roasting tray. Cut the tops off the garlic heads so that each clove has an escape hatch and throw the heads in the tray. Toss everything with olive oil and seasonings (I used salt, pepper and mustard powder). Put the tray under the broiler/grill in the oven and brown the shanks for a few minutes, stopping once to flip them. (If you don't have a broiler/grill, you could preheat your oven on its highest baking temperature.) Cover the tray tightly in foil to trap steam, reduce heat to 285ºF/140ºC, and roast slowly until the meat is ready to fall off the bone and the garlic is soft and golden — mine took 4 hours.
3. While you're waiting you can make the celery root purée. Peel the celery root and then cut it into small pieces (grating it with the large holes on a box grater might be even better). Melt some butter into a pan (enough to generally coat), dump in the pieces, and cook for about 10 minutes, stirring frequently, until the pieces have softened a bit — stop before anything gets very brown. Pour in just enough milk to cover everything, reduce the heat to low, cover and simmer until the pieces are soft — I did an hour but that was probably overkill. The milk will curdle during cooking, FYI.
4. Strain/pour any loose liquid out of the pan and reserve it. Dump the solids in a food processor and blitz until as smooth as possible — add back in any liquid to get the texture you want. Mix in salt and cayenne to taste, along with a squeeze of lemon (that's mostly to reduce enzymatic browning). You can reheat this in the microwave when it's time to eat. If you have any more reserved liquid, you can use that in the lamb sauce.
5. When the lamb is done, transfer the shanks to a baking sheet and set aside. Remove the garlic heads and set aside. Put the baking tray on a burner and boil off the water from any accumulated meat juice sloshing around under the rendered lamb fat. Pour the fat off and discard (or save for roasted potatoes another day) while keeping all the other brown bits in the tray. Squeeze in the roasted garlic. Deglaze the pan with the reserved liquid from the celeriac, or use wine/water/whatever. Mash up the garlic cloves and add more liquid if necessary to get the sauce texture you want. You could strain it at this point if you want it to be extra-pretty.
6. Taste the sauce for seasoning and adjust. Turn the heat off, and when the bubbling has stopped, slowly melt in as much butter as you want to enrich and thicken the sauce a bit. Finish with lemon juice to taste.
7. When you're ready to eat, return the lamb shanks to the oven and increase the temperature to 400ºF/200ºC. Roast them another 5 minutes or so just to crisp their exteriors. You could steam a green veggie at this point, as I did with some broccolini. Plate everything up and top with sauce.