Step 1

Melt butter in a medium saucepan over medium-low. Add onion and jalapeños. Cook, stirring occasionally, until softened, about 5 minutes. Add green chiles and garlic. Cook, stirring occasionally, 30 seconds.

Step 2

Whisk together milk, 1 cup water, and cornstarch in a bowl until well combined. Add to chile mixture in saucepan. Bring to a simmer over medium-low, stirring constantly. Continue cooking, stirring constantly, until mixture thickens, 5 to 7 minutes. Add cheese; reduce heat to low, and cook, stirring occasionally, until cheese is melted, about 2 minutes. Stir in cilantro, cumin, salt, and cayenne. (Add additional seasoning, if desired.)

Step 3

Transfer queso to a serving bowl, small slow cooker, or chafing dish set over a flame. Sprinkle with cilantro. Serve queso warm with tortilla chips, guacamole, and pico de gallo.