Add the chicken broth, soy sauce and sliced onion to slow cooker and give it a stir.
First, mix salt, pepper, garlic powder, and onion powder. Rub this mixture all over the pork loin.
Heat a large skillet for several minutes over medium-high heat then add oil.
Once the oil is shimmering hot, sear the pork loin on all sides until it's golden brown, about 3 minutes per side.
In a small bowl, whisk together the balsamic vinegar, honey and garlic.
Place the pork loin on top (fat-side up) of the onions and brush the pork all over with this balsamic vinegar mixture.
Cook on low for 6-8 hours or on high for 3-4 hours. Once it's done, the pork will be fall-apart tender and delicious. Transfer pork to a serving platter.
Whisk butter into the liquid left in the slow cooker. This turns it into a glossy sauce to serve with the pork.Give it a taste and add a bit more salt and pepper if desired (mine usually needs a pinch more of both).Serve pork with the sauce on the side.
