To make the green-chile Mornay sauce, roast the poblano and jalapeño chiles under the broiler until blackened, about 5 minutes per side. Place the chiles in a paper sack or plastic food-storage bag, close it tight and let the chiles steam for 20 minutes. Take the chiles out of the bag and rub off the skin. Remove seeds and stems and dice.
In a saucepot, on low heat melt the butter. Add the onions and while stirring occasionally cook until onions and jalapeños are softened, about five minutes. Add the garlic and cook for 30 more seconds. Whisk in the flour and cook until it’s well incorporated and a light-brown paste forms, about 1 minute.
Pour in the half-and-half, turn up the heat to medium high, and while whisking bring the sauce to a boil. As it boils, continue to whisk until it thickens, which can happen anywhere from immediately to a minute. After it thickens, turn the heat back down to low.
A handful at a time, whisk in the white cheddar and the Muenster, waiting until it melts before adding more. Once the cheese is incorporated, stir in the diced green chiles, cilantro, cumin, and cayenne, and add salt to taste. If the sauce seems too thick, you can thin it with more half-and-half.
To assemble the sandwiches, turn on the broiler. Cut the bolillo rolls in half, lengthwise, and place each under the broiler until lightly toasted, about 20-30 seconds. Remove from the oven.
On a rimmed oven-safe plate or small skillet, place a toasted roll half. Spread on the roll 2 tablespoons of refried beans. Top the beans with 1/4 of the roasted turkey. Pour over the sandwich some of the green-chile Mornay sauce and sprinkle with some of the cooked bacon and tomatoes. (Any leftover sauce will go dandy with some tortilla chips.)
Place the sandwich under the broiler and cook until the sauce begins to brown and bubble, about 1 to 2 minutes. For serving, top the sandwich with a scoop of guacamole and a shower of Cotija cheese. Repeat for the other sandwiches. (Depending on the size of your oven, you can broil several sandwiches at a time.)
Tex-Mex hot brown sandwich with green chile Mornay sauce | www.homesicktexan.com