In a small bowl, combine a couple of large spoonfuls of orange marmalade, one large spoonful of a coarse-grained mustard, about one teaspoon of dried thyme, and about half a teaspoon of black pepper. Stir it well.
Rinse a center-cut pork tenderloin and pat dry. Sprinkle with salt, pepper, and dried thyme. Heat oil in a large skillet over medium-high heat, and brown tenderloin quickly on all sides. Remove from heat.
Add a bit more oil to the pan and reduce heat to low. Thickly slice one large onion and add to pan. Slowly cook onion until soft, but not browned.
Place pork tenderloin in a 9 x 13" pan and coat with glaze. Smother with onions.
Bake at 375 degrees, basting occasionally with glaze, for about 45-60 minutes, or until juices no longer run pink. Remove to a cutting board and let rest 5 minutes before slicing.
Will serve 4 grateful family members