Melt the butter over medium heat in a medium saucepan for about 30 seconds until it's foaming and fragrant.

Add the finely diced white onion and cook for 3 to 4 minutes, stirring often, until the onion becomes soft and translucent.

Lower the heat to the lowest setting and pour in the heavy cream, stirring with a whisk to combine. Let this warm gently for about 1 minute without letting it simmer.

Add the shredded sharp cheddar cheese in two batches, stirring constantly with a whisk after each addition until the cheese melts completely before adding more.

Stir in the Oaxaca or mozzarella cheese one small handful at a time, whisking constantly until each addition melts fully.

While the cheese is melting, combine the minced chipotle peppers, adobo sauce, cumin, and garlic powder in a small bowl and stir them together.

Pour the chipotle mixture into the melted cheese and stir gently with a wooden spoon, folding it in for about 1 minute until the color is even.

Taste the queso and add salt and pepper gradually until the flavors pop without being salty.

Pour in the fresh lime juice and fold in the chopped cilantro gently just until combined.

Carefully pour the hot queso into a serving bowl or small cast-iron skillet to keep it warm at the table.