Grate the cheeses and set them aside in a bowl. Drain the diced tomatoes if using. Chop the onion, jalapeño, and garlic so everything’s ready to go.

In a medium saucepan over medium heat, melt the butter.

Add the diced onion and sauté for 3–4 minutes until softened and translucent.

Stir in the jalapeño and garlic and cook another 30–60 seconds until fragrant.

Sprinkle the flour over the onion mixture and stir continuously for about 1 minute.

Slowly pour in the milk while whisking constantly to avoid lumps. Whisk until the mixture thickens slightly—about 2–3 minutes.

Stir in the half-and-half.

Lower the heat to medium-low. Add the shredded cheeses a handful at a time, stirring until each addition is smooth before adding more.

Stir in the cumin, smoked paprika (if using), and drained diced tomatoes. Taste and adjust salt and pepper.

Transfer to a serving bowl, sprinkle with chopped cilantro, and set out a big basket of tortilla chips.

For a party, keep the queso warm in a small slow cooker at the lowest setting.