To make the lemon confit butter, place the butter in a medium bowl. Quarter the lemon and remove and discard any interior pulp. Using a small sharp knife, remove and discard any white pith, leaving just the zest, the deep yellow part of the rind. Finely mince the zest. Using a wooden spoon, incorporate the lemon zest into the softened butter. Season with a pinch of salt. To store the butter, transfer it to a sheet of parchment paper. Fold over half the parchment lengthwise and shape the butter into a log using a bench scraper, keeping an even thickness throughout. Twist the ends in opposite directions to secure. Wrap tightly with plastic wrap and refrigerate for up to 2 weeks. The butter can also be frozen for up to 2 months. Bring to room temperature before using.

Remove the pork loin from the refrigerator and let it come to room temperature before searing, about 1 hour.

Preheat an oven to 400°F (205°C).

Pat the loin dry. Using butcher’s twine, tie the loin to secure the meat for even roasting. Dry the meat well with paper towels and season liberally with about 1 Tbs. salt.

In a large oval or other roasting pan over medium-high heat, heat the olive oil until hot but not smoking. Turn the pan to coat it evenly with the oil, then add the loin and sear, turning occasionally, until browned and caramelized on all sides, 8 to 10 minutes. Transfer the loin to a cutting board and let rest about 5 minutes, until comfortable to touch.