Season the pork well on both sides with salt and pepper.
Next heat the oil in a large cast iron skillet over medium-high heat and add in the pork.
Immediately add in 2 ounces of unsalted butter, thyme and garlic cloves and cook until the pork is golden brown, about 4 to 5 minutes before flipping it over.
Baste the pork constantly with the butter in the pan until it is browned all the way around and a medium to medium-well internal temperature is achieved, about 5 to 7 more minutes.
Remove the pork from the pan discard the butter, thyme and garlic in the pan, and then return the pan to the burner over medium heat.
Add in 1 ounce of butter and cook the onions until they are lightly browned, about 5 minutes. Next, add in the fennel and apples and cook for 3 to 4 minutes. Add in the sugar and cook for 2 minutes before deglazing with the apple cider vinegar.
Finish the mixture with salt, pepper and remaining 3 ounces of butter.