Sweet roast pork with lentils

This dish was judged a little too sweet by some, but is really easy to make so I'll share it anyway and let you be the judge.
Cut 4 peeled onions roughly into eights. Put in a dish with 4 minced garlic cloves and 1 cup (~2 dl) of dry French lentils. Pour over 1 cup (~2dl) of apple cider, and place a pork tenderloin (~450 gr) on top. Make a few diagonal, shallow, cuts in the meat and cook at 180 C/ 350 F for 50 minutes. Add another cup of cider, and cook for another 45 minutes or until the pork is at temperature and the lentils are soft. If the meat cooks quicker than the lentils, remove it and keep it warm while you cook the lentils another 15 minutes or so, adding hot water if needed.