Shred both cheddar and Monterey Jack cheeses using a box grater and let them come to room temperature. Dice the onion finely, mince the garlic, chop the chipotle peppers into small pieces, and cube the cream cheese into small chunks.

Melt the butter in a medium saucepan over medium heat. Add the diced onion and cook for 3 to 4 minutes until softened and translucent. Add the minced garlic and cook for another 30 seconds, stirring constantly.

Sprinkle the flour over the butter, onion, and garlic mixture, stirring constantly for about 1 minute until the flour is cooked but not browned.

Slowly pour in the milk while whisking constantly to prevent lumps. Once the milk is fully incorporated, add the heavy cream and continue stirring. Bring the mixture to a gentle simmer and let it thicken for about 2 minutes, stirring frequently, until it coats the back of a spoon.

Reduce the heat to low and add the cream cheese cubes, stirring until completely melted. Add the shredded cheddar and Monterey Jack in three batches, stirring each addition until fully melted before adding more.

Stir in the chopped chipotle peppers, adobo sauce, cumin, smoked paprika, and salt. Mix thoroughly so the spices and peppers distribute evenly. Taste and adjust heat level if desired.

Give the cornstarch slurry a quick stir, then pour it into the queso while stirring constantly. Let the mixture simmer for 1 to 2 minutes until it thickens to desired consistency.

Transfer the queso to a serving bowl and top with chopped fresh cilantro if using. Serve immediately with tortilla chips. For parties, transfer to a small slow cooker set on warm to maintain perfect dipping consistency.