Step 1

Open the package of pork and remove one tenderloin. Save the second for another meal. Place the pork on a large plate.

Step 2

Mix together the salt, rosemary, celery seed, black pepper, and minced garlic in a small bowl.

Step 3

Rub the pork all over with the olive oil and then coat it well with the spice mixture on all sides.

Step 4

Place the sliced onion on the bottom of the slow cooker, favoring one side of the slow cooker, and then place the pork on top of the onion.

Step 5

Gently drizzle the soy sauce and Worcestershire sauce over the pork.

Step 6

Use a large piece of foil to make a pocket for the potatoes next to the pork. Be careful to make it large enough so that the pork juice won’t get into the foil.

Step 7

Fill the foil with the cubed potatoes and add 1 tablespoon of butter.

Step 8

The pork should be off to one side but not completely touching the side of the slow cooker.

Step 9

Add the lid and cook for 3.5 to 4 hours on LOW or until the pork registers 145 degrees using an instant-read thermometer or the probe on your slow cooker.

Step 10

When the pork is cooked through, remove from the oven and allow to rest for 3 minutes.

Step 11

While the pork is resting, place the potatoes in a large bowl and add the remaining 2 tablespoons of butter, chopped parsley and salt to taste. Stir to combine.

Step 12

Slice the pork and place it on a serving platter. Serve right away with buttered potatoes on the side.