If starting with fresh Hatch chiles, roast them under a broiler, over a gas flame, or on a grill until the skins are blistered and blackened on all sides. Place the hot chiles in a covered bowl or sealed bag for 10–15 minutes, then peel, stem, seed, and chop them while wearing gloves.

Heat the oven to 375°F and grease an approximately 8 x 8-inch baking dish. Drain the chopped roasted chiles thoroughly so excess liquid does not make the dip thin or greasy.

Beat the softened cream cheese with the sour cream and mayonnaise until mostly smooth. Stir in the chiles, garlic, cumin, salt, black pepper, optional jalapeño, and optional green onion or cilantro.

Add about three-quarters of the shredded cheddar and Monterey Jack, stirring until evenly distributed. Spread the mixture into the prepared baking dish and sprinkle the remaining cheese over the top.

Bake for 20–25 minutes, until the dip is hot, bubbling, and lightly browned. Broil for 1–2 minutes if you prefer a more deeply browned cheese topping, watching closely so it does not burn.

Let the dip rest for 5 minutes before serving. This short rest allows the creamy mixture to thicken slightly while keeping the cheese warm and scoopable.