Arrange a rack in the middle of the oven and heat the oven to 400°F.
Trim the silverskin ( I keep the fat cap intact). Pat dry loin well with a kitchen towel. I prefer trussing the loin so that it holds shape and cooks evenly. (Watch the video at the end where I have shown how to truss pork loin)
Season generously with salt and pepper on both sides.
Heat an oven-proof skillet. Add 2 tablespoons of oil/butter. Sear all 4 sides on medium-high heat for 3-4 minutes, until it forms a light brown crust. (while searing, it might splatter oil so be careful)
Remove seared loin, keep aside covered.
To the same skillet in the remaining oil, add slightly crushed whole garlic, onion wedges, rosemary, and thyme. Stir well and saute onion for a couple of minutes until lightly browned around the edges.
Add apple wedges, apple juice, dijon mustard, brown sugar, salt and pepper. Give everything a good stir. Arrange apple and onion wedges in a single layer (making a bed for the pork loin to sit).
Place seared pork loin on top along with any juice from pork in the plate. insert a meat thermometer at the center. Roast the pork loin until an instant-read thermometer inserted into the thickest part registers at least 130°F, for about 30-35 minutes. (ref note 1).
Once done carefully remove the thermometer and loosely cover it for 15-20 minutes before slicing.