01 -
Spray a 6 to 8-quart slow cooker with cooking spray and layer the sliced onions evenly at the bottom.
02 -
Pat pork tenderloins dry and season all sides with salt and black pepper.
03 -
Heat olive oil in a large skillet over medium-high heat. Sear each tenderloin on all sides until evenly browned, about 2-3 minutes per side.
04 -
Place seared tenderloins on top of the onion bed in the slow cooker. Pour beef broth around the meat, avoiding pouring directly over it.
05 -
Sprinkle pork gravy mix evenly over the tenderloins. Distribute butter slices atop the pork.
06 -
Cover and cook on low heat for 2 to 2½ hours or until the internal temperature reaches at least 145°F and onions are tender.
07 -
Slice tenderloin and serve immediately, spooning the cooking juices over the slices as gravy.