In a small bowl, toss cheese and cornstarch. Set aside.
In a medium saucepan, melt butter over medium heat. Add garlic and onion and cook slowly for 3 minutes. Add drained tomatoes and cook 2 minutes.
Add evaporated milk and cheese, Stir in chiles and spices. Continue stirring until cheese melts and becomes a silky sauce. Add cilantro
Stir in milk, as needed, to adjust consistency. Dip will thicken as it cools.
Remove from heat and serve.
Store leftover queso dip in the refrigerator. Dip will thicken when cool. Reheat in microwave adding additional milk as needed.