Wash the poblano chiles and roast directly on a gas flame or under a broiler.
Once the chiles have blistered and blackened, wrap them in a clean cotton towel and cover with a glass bowl. Allow to steam for about 20 minutes.
Remove them from the towel and carefully peel the chiles. You can use a paring knife to scrape off any loose peel.
Slit the chile lengthwise, turning out the interior bulb of the stem where the seeds are attached.
Remove the seeds either by scraping them out or by cutting out the bulb, while leaving the stem intact. Set aside.
In a 10-inch skillet, brown the ground pork, beef, and minced onion.
Once the meat is no longer rare, add the remaining ingredients and allow to simmer for about 20 minutes.
To make the sauce, melt the butter in a separate 10-inch skillet.
Add all the nuts and allow to brown for about 7 minutes over medium heat; make sure they do not scorch.
Once browned, add the nuts to a food processor or blender (or use an immersion blender) and puree, adding the half and half as necessary to make a sauce that is the consistency of a thick, warm salad dressing.
Return the sauce to the pan, salt to taste, add any remaining half and half and the queso cotija, and heat gently for about 10 minutes as you prepare the chiles.
Fill each of the chiles with a couple of spoonfuls of the meat mixture and place on a platter with the open slit to the side or underneath.
Do not overfill. (If desired, stuff chiles and rewarm in a 350-degree oven for about 10 minutes.)
Once your platter of chiles is ready, top with the warm sauce and garnish with the pomegranate seeds.