In a small bowl, whisk together the cornstarch and 2 tablespoons of water until smooth. Set aside.
Heat evaporated milk in a medium saucepan over medium-low heat. Warm the milk until you see light steam and small bubbles forming around the edges. Do not let it boil.
Whisk the cornstarch slurry into the warm milk. Then add the shredded cheese in batches, stirring each batch until it fully melts before adding the next. Keep the heat low to prevent the cheese from curdling
Once the cheese is fully melted and smooth, stir in the onion powder, garlic powder, and chili powder. Taste and add a pinch of salt if needed.
Transfer the queso to a serving bowl and top with your favorite toppings. Serve warm with tortilla chips.
Notes
*Don't use pre-shredded cheese in your queso. Often, prepackaged shredded cheese is coated with anti-caking agents, which prevent it from melting smoothly. You'll need to shred the cheese yourself for the best results.