Melt butter in a large skillet over medium-high heat. Add onion; sauté 3 minutes or until tender. Add garlic; sauté 1 minute. Reduce heat to medium; stir in cheese dip, chiles, and cumin, stirring constantly until cheese melts. Serve warm with tortilla chips, or spoon dip into small jars or containers. Cover and chill. Give jars of dip as gifts along with reheating instructions.
Note: To reheat 1 cup dip, place in a microwave-safe bowl. Microwave dip on HIGH for 3 minutes, stirring after 1 1/2 minutes.