Cut beef into 1-1/2-inch pieces. Place in a plastic bag set in a deep bowl.
In a blender container or food processor bowl place onion, the 2 tablespoons soy sauce, lime juice, sugar, cumin, and 1 clove garlic. Cover and blend or process until smooth. Pour over meat in bag; close bag.
Marinate meat in the refrigerator for 4 hours, turning bag occasionally. Drain meat, reserving marinade.
In a saucepan stir broth into peanut butter. Stir in molasses, the 1 teaspoon soy sauce, crushed red pepper, and 1 clove garlic. Cook and stir until heated through. Keep warm.
Thread meat onto four 8-inch skewers. Arrange on the unheated rack of a broiler pan. Broil 3 to 4 inches from the heat for 7 to 9 minutes or to desired doneness (160 degrees F for medium doneness), turning occasionally. Serve sauce with meat for dipping. Makes 4 servings.