- Preheat oven to 160°C (325°F).
- Take meat out 20–30 minutes before cooking and let stand until it reaches room temperature. Take the point of a knife and make shallow incisions in the fatty side of the meat every 5 mm (¼ lb.) across its width. Season generously with salt and pepper.
- To make the sauce, squeeze the garlic head to extract the grilled garlic and crush each clove.
- Combine grilled garlic, oil, Dijon mustard, maple syrup, lemon zest, and tarragon in a small bowl.
- Add salt and pepper to taste.
- Mix well and set aside.
- Heat a grill pan or other large cast iron skillet on high.
- Place loin in skillet and grill on both sides.
- Transfer pork to a drip pan, fatty side up, and bake 20–25 minutes per 450 g (1 lb.), around 1 hour and 40 minutes total.
- Take pork from oven and cover with aluminium foil.
- Let stand for 5 minutes.
- Cut loin diagonally in 1 cm (½ in.) slices.
- Drizzle tarragon sauce over pork.
- Serve with garlic accordion potatoes and grilled parsnip.
To cook the pork to perfection, take it out of the oven before it reaches the desired temperature. Cover and let stand: the temperature will continue to increase by a few degrees. For slightly pink pork, insert a meat thermometer in the centre of the loin. The temperature must reach 70°C (160°F).
To make accordion potatoes, thinly slice potatoes along their width three quarters of the way through and insert thin slices of garlic with butter and fine herbs. Drizzle with a little olive oil. Bake at 200°C (400°F) for 40 minutes.