In a large skillet, melt the 2 tablespoons of unsalted butter over medium heat. Add the chopped onion and sauté for about 5 minutes until it becomes translucent. Toss in the jalapeños and minced garlic, cooking for another 2-3 minutes until fragrant.
Stir in the pickled Serrano chiles (if using) and halved cherry tomatoes. Cook for another 2 minutes, just until the tomatoes start to soften.
In a separate bowl, whisk together the evaporated milk, cornstarch, and water until smooth. Pour this mixture into the skillet with the sautéed vegetables, stirring well to combine.
Gradually add the grated yellow and white American cheese to the skillet, stirring continuously until the cheese is completely melted and the mixture is smooth. This should take about 5-7 minutes over medium-low heat.
Once the cheese is melted, stir in the ground cumin, onion powder, black pepper, and Kosher salt. Then, mix in the can of green chiles, stirring to combine everything thoroughly.
Remove the skillet from the heat and stir in the fresh cilantro. Transfer the queso to a serving bowl and garnish with Pico de Gallo. Serve warm with tortilla chips for dipping!
