Preheat an oven to 350 degrees F (175 degrees C). Grease a baking
dish large enough to hold the tenderloin without folding it.
Heat the olive oil in a large skillet over medium-high heat, and
brown the pork tenderloin on all sides. Remove the browned
tenderloin to the prepared baking dish. Sprinkle all sides of the
meat with salt, pepper, and parsley.
Cook and stir the onion and apple in the same skillet over medium
heat until the onion becomes soft, about 5 minutes, and pour in the
Riesling wine
Scrape all the browned flavor bits off the bottom of
the skillet and stir to help dissolve them into the wine. Bring to a
boil, and pour the onion, apple, and wine mixture over the
tenderloin.
Mix together the apple jelly and balsamic vinegar in a bowl until the
mixture is smooth and without lumps. Spread the jelly mixture all
over the pork
Bake the loin in the preheated oven until an instant-read
thermometer inserted into the center reads 160 degrees F (70
degrees C), 30 to 45 minutes
Allow the tenderloin to rest for 10 minutes before slicing, and serve each slice with a spoonful of the
apple-onion mixture