Preheat your oven to broil. Place the Hatch chiles on a baking sheet and broil them for about 20 minutes, turning occasionally until the skins blister and char. Once roasted, transfer the chiles to a bowl, cover them with plastic wrap, and let them steam for 10 minutes.

In a large skillet, heat 2 tablespoons of olive oil over medium heat. Add the finely chopped white onion and optional jalapeño, cooking for about 4-5 minutes until softened and translucent. Stir in minced garlic and sauté for an additional minute until fragrant, then remove from heat.

Sprinkle 2 tablespoons of all-purpose flour over the sautéed mixture in the skillet. Stir continuously for about 2 minutes without browning it to create a roux.

Lower the heat to medium-low and slowly stir in one can of evaporated milk, mixing well. Season with salt and black pepper to taste. Gradually add in 3 cups of your favorite melting cheese, stirring until fully melted and smooth.

Carefully peel the skins off the roasted chiles, remove seeds, and chop them into small pieces. Mix into the cheese dip, adjusting consistency with additional milk if too thick.

Remove from heat, transfer to a serving bowl, and garnish with fresh cilantro or green onions. Serve hot with tortilla chips.