for the mustard sauce: In a small bowl, combine all mustard sauce ingredients. Set aside.

for the pork loin roast: Pat the pork loin dry using paper towels. With kitchen string, tie up the pork loin every 2 inches. Reference the photo from this post that shows how this should look.

Create a simple garlic paste by sprinkling the salt over the minced garlic, right on the cutting board. Angle the knife blade (I like to use a knife with a larger blade, such as a Santoku knife or chef's knife.) so it's laying almost flat on the cutting board, pressing and scraping the garlic and salt together. The garlic pieces will start to soften and smash, and combine with the salt to form a paste. Keep pressing and scraping until you have a smooth paste. Sprinkle pepper over the paste, and then press and scrape a few more times to incorporate. Rub this mixture over all sides of the pork loin. Set aside at room temperature.

Preheat oven to 350° F.

Place a 12" cast iron skillet or stainless steel straight-sided skillet on stovetop and heat to medium-high. Add canola oil and heat until shimmering. Carefully add pork loin, fat cap side down. Sear until deep golden brown and when it releases easily from the skillet, about 4 to 5 minutes per side. Once all four sides have browned, transfer pork loin with the fat cap facing up to a rack set inside a roasting pan. If you do not have one of these, simply place a cooling rack inside a large rimmed pan. I like to line my rimmed pan with aluminum foil for easy clean up.

Brush seared pork loin on all sides with mustard sauce, using all of the sauce for a 3-1/2 pound pork loin. Tent a large piece of aluminum foil (I like these extra large, heavy duty rolls) loosely over the pork loin, keeping the foil from touching the pork. Cook for 35 minutes. Remove foil tent and cook for another 15 to 20 minutes or so, or until an instant-read thermometer inserted into the thickest part of the pork reads 145° F. I start checking the temperature after the pork has cooked for 10 minutes without the foil tent. Do not over cook. Remove pork loin from oven and let rest 3 minutes. Remove kitchen string and slice pork loin crosswise into 1/2-inch slices. Serve hot, sprinkled with minced fresh rosemary and parsley if desired.