Pat dry the pork loin with a paper towel, discard towel into trash.
Brush 1 tablespoon of olive oil over all sides of loin.
Combine brown sugar, paprika, salt and pepper in a small bowl to create dry rub.
Sprinkle the dry rub over the pork loin.
Warm remaining tablespoon of olive oil in a cast iron skillet or a heavy-bottomed skillet using medium heat.
Place the pork loin in the heated skillet and sear, turn after 2-3 minutes per side.
Transfer the pork loin to the slow cooker.
Save drippings from the searing process in the skillet and add in one stick of butter, melt using low heat.
Increase to medium-high heat, stir in garlic and onions. Cook for one minute or until golden.
Stir honey and vinegar in to the sauce mixture and bring to a slow boil for 30 seconds.
Remove skillet from heat and pour sauce over the pork loin inside the slow cook.
Place lid on slow cooker and cook on low for 3 1/2 to 4 1/2 hours.
Pour juices from the slow cooker into a sauce pan, turn on medium heat and stir.
In a glass measuring cup mix 1 tablespoon of cold water with 3 teaspoons of corn starch.
Slowly incorporate the corn starch slurry into the simmering sauce pan and stir.
Bring the liquids up to a slow boil for 5 minutes or until syrupy consistency.
Reduce the heat and serve the sauce over the top of the sliced pork loin.