1 medium tomato
1 1/2 tablespoons butter
1/2 cup finely chopped onion
1 can (4oz) chopped mild green chilies
2 cloves garlic, minced
1/2 teaspoon mild chili powder
1 teaspoon cornstarch
1/2 cup milk or half-and-half
3 cups (about 12oz) grated sharp Cheddar (for a milder flavor, substitute up to half Monterey Jack)
Salt and ground black pepper, to taste
Tortilla chips, for serving
Slice the tomato in half crosswise and squeeze each half to force out the seeds or simply push out the seeds with a clean finger. Coarsely chop the tomato and set it aside.
Melt the butter in a large saucepan and add the onion, green chilies, garlic, chili powder, and tomato. Saute the vegetables over medium-low heat, stirring often, until the vegetables are softened, about 5 minutes.
The next step requires constant stirring as each ingredient is added, to ensure a smooth, thick sauce with no lumps. First, stir in the cornstarch, then the milk or half-and-half. Cook, stirring constantly, until the liquid is barely simmering, about 2 minutes; it will thicken slightly. Stir in half of the cheese and continue to stir until the cheese is melted, about 2 minutes; do not let the mixture boil. Add the remaining cheese and continue to stir until the cheese is melted and heated through, about 2 minutes. Taste, and add a little salt and pepper, if necessary.
Pour the dip into a heated serving dish or a small, heated slow-cooker. Serve hot, with tortilla chips. Serves 10 as an appetizer.