Step 1

Place the cornstarch in a small bowl. Add a few tablespoons of evaporated milk to the bowl and whisk to dissolve the cornstarch. Set aside.

Step 2

In a small saucepan, melt the butter over medium heat. Add the onion and cook until just starting to soften, about 3 minutes. Stir in the chiles, garlic, and cumin. Cook for 2 minutes.

Step 3

Pour in the remaining evaporated milk and whisk in the cornstarch mixture. Bring to a simmer and cook until thickened, about 4 minutes.

Step 4

Adding a small handful at a time, slowly whisk in the cheese, until incorporated and all of the cheese is melted. Stir in the tomatoes and add salt to taste. Serve immediately topped with chopped cilantro, diced tomatoes, and sliced jalapeños, if desired.