Pat the pork completely dry with paper towels and season all sides generously with kosher salt and pepper — don't skimp on the edges, that's where most of the crust forms.
Heat olive oil in a large Dutch oven over medium-high heat until it shimmers but doesn't smoke. Sear the pork on all sides until deeply browned, about 8 minutes total. Remove and set aside.
Reduce heat to medium. Add onions to the pot and cook, stirring occasionally, for 5 minutes until they begin to soften and release their juices.
Add apple wedges and thyme; stir once more so everything gets coated in the pan drippings.
Place pork back into the pot, nestling it among the fruit and vegetables. Pour in apple cider — you want enough liquid to come about a third of the way up the sides of the roast.
Cover tightly with lid or foil and transfer to a 325°F oven. Cook for about 4 hours until internal temperature reaches 145°F at the thickest part (I check with an instant-read thermometer).
Remove from oven, tent loosely with foil, and rest for 15 minutes before slicing against the grain.
