- Preheat oven to 250°C (450°F).
- Make about 12 incisions ½ cm (¼-in.) deep in the fat on the rack of pork and insert the slices of garlic inside.
- Mix together the herbes de Provence, pepper, cayenne pepper, salt, and mustard in a bowl.
- Spread the mixture over the entire rack of pork.
- Mix together the onions, garlic, salt, and olive oil in a large bowl. Line a 30 x 45 cm (12 x 18 in.) drip pan with parchment paper and place the onions on it. Place the rack of pork on top of the onions.
- Bake in the oven for 15 minutes and then reduce oven temperature to 200°C (400°F). Bake until internal temperature reaches 68°C (155°F), about 1 hour and 15 minutes.
- Stir the onions once or twice while cooking and cover the rack of pork with a sheet of foil when the spice crust starts to brown.
- Combine the squash and herbs with a drizzle of olive oil in a bowl. Season with salt and pepper to taste.
- Add seasoned squash to the rack of pork for the last 20 minutes of cooking.
- Remove from oven. Cover rack of pork with a sheet of foil and let stand for 5 to 15 minutes (keep vegetables warm in the oven that's turned off during this time).
- Serve the rack of pork with mashed potatoes and carrots topped with onions, squash, and Dijon mustard, if you like.
To prepare the mashed potatoes and carrots, cook them in boiling salted water with 3 or 4 cloves of garlic and a bay leaf before mashing with a potato masher.