1/4 cup butter or margarine
1/2 cup finely chopped onion
1 can (about 15 ounces) diced tomatoes with liquid
2 cans (4 ounces each) chopped mild green chiles, drained
1/2 teaspoon salt
16 ounces Monterey Jack cheese, cubed
1/2 cup heavy cream

In a large skillet over medium low heat, melt butter. Sauté onion until tender. Add tomatoes, chiles, and salt, mashing tomatoes with a fork. Simmer, stirring a few times, for about 15 minutes. Add cheese cubes, stirring until cheese is melted. Stir in cream. Continue to cook, stirring constantly, for 2 minutes longer. Remove from heat and let stand for 10 minutes. Serve in chafing dish, slow cooker, or other dish with heat. Serve chile con queso dip with corn chips or vegetable dippers. Sauté a little chopped jalapeno or serrano pepper with the onion for hotter dip.