Melt the butter in a saucepan over medium heat.
Add the chopped onion and sauté until translucent, about 5 minutes.
Stir in the minced jalapeños and garlic; cook for another 2-3 minutes.
Sprinkle in the cumin and paprika, stirring until fragrant, about 1 minute.
Pour in the whole milk, stirring to combine.
Gradually add the Monterey Jack and cheddar cheese, stirring until melted and smooth.
Season with salt and pepper to taste, adjusting as necessary.
Serve warm with tortilla chips or as a topping for your favorite dishes.