Sauce: Place everything for the sauce in a saucepan and turn heat to high. Allow the sauce to come up to a boil and cook for about 5 minutes, or until the cranberries start to pop. Reduce heat to medium and allow sauce to simmer for an additional 5-10 minutes, or until it starts to thicken and all the cranberries have burst. (Note: You can make this sauce ahead of time, and if you want your sauce to be smooth, you can blend it after cooking.)
Tenderloin: Heat the skillet over medium high heat. Pat the meat dry with paper towels to make sure it gets browned. Season the tenderloin with seasonings, and cook for about 1 minute on all of the sides until it is lightly browned.
Crockpot Cooking: Spray crockpot with cooking spray and place tenderloin in crockpot. Pour 1/2 of the cranberry sauce over the tenderloin, (save the other half for serving). Cover and cook on high 4 hours, or on low 8 hours, or until meat is fully cooked through. Top or serve with leftover cranberry sauce and enjoy!
Oven Cooking: Preheat oven to 425 degrees. Roast the tenderloin in preheated oven for 25 to 30 minutes, or until the meat reaches an internal temperature of 165 degrees in the thickest part of the turkey tenderloin (or at least 145 degrees for pork tenderloin). When it is fully cooked, remove it from the oven and allow it to rest, brushing with juices from the bottom of the pan. Top or serve with leftover cranberry sauce and enjoy!