In a shallow bowl, combine flour, salt if desired and pepper.
Cut each tenderloin into six pieces; flatten to about 1-in. thickness. Melt butter in a large skillet. Dip pork into flour mixture; add to skillet and brown on both sides.
Place in an ungreased 11x7-in. baking pan. In the same skillet, saute onion and garlic until tender.
Add remaining ingredients; bring to a boil.
Pour over pork. Cover and bake at 350° for 1 hour or until the juices run clear and a thermometer reads 160°.