Step 1

Combine soy sauce, bourbon and brown sugar in a large Ziploc bag or dish. Add pork to the marinade and refrigerate for at least 1 hour (or up to overnight).

Step 2

Place a large cast iron (or other oven-safe) skillet in a cold oven. Preheat the oven (and the skillet) to 450 degrees F.

Step 3

Remove the pork from the marinade. Pat dry; season liberally with salt and pepper on all sides.

Step 4

Carefully remove the hot skillet from the oven. Add 1-2 teaspoons of vegetable oil to the skillet and swirl to coat the bottom of the pan. Place the pork in the skillet and return to the oven for 10 minutes. Turn the pork over, reduce the oven temperature to 400 degrees F, and continue roasting the pork for about 10-15 more minutes. The pork is done when it reaches an internal temperature of 140-145 degrees F in the thickest part (about 20-25 minutes total).

Step 5

Allow the pork to rest for 5-10 minutes before slicing. Meanwhile, prepare the mustard sauce.

Step 6

In a small bowl, stir together the sour cream, mayonnaise, Dijon and rosemary. Serve with sliced pork.