I really don't know if this is considered a holiday dish down here but I have only seen the Pomegranates in December here in the grocery stores. And with all of the steps it is not an everyday dish. I have also noticed ladies buying alot of the same ingredients so I can only surmise that this is a Nochebuena favorite in our area.
Chilies En Nogada
The recipe is said to have been concocted by the grateful people of Puebla, who were giving a banquet in honor of Don Agustin de Iturbide's saint's day, August 28 in 1821. He and his followers had led the final revolt against Spanish domination; as self-proclaimed emperor he had just signed the Treaty of Cordoba. All the dishes at the banquest were concocted of ingredients of the color of the Mexican flag; in this dish were the green chilies, the white sauce, and the red pomegranate seeds. Many favorite dishes here in Mexico have the Bandera national colors.
You must start this dish one day ahead by soaking the walnuts for the nogada sauce overnight. This dish is a bit involved, but the effort is worth it. It really is an extraordinary blend of flavors. But if you get an opportunity to order it in a restaurant without all the prepration by all means taste & enjoy the flavors.

The Picadillo:
2 lbs of ground pork or beef
1/2 onion, sliced
1 Tbsp salt, or to taste
Put meat into the pan with the onion, garlic, and salt and cover with cold water. Bring the meat to a boil, lower the flame and let it simmer until just tender - about 40-45 minutes. Do not over cook. Leave the meat to cool off in the broth.
Strain the meat. Let the broth get completely cold and skim off the fat.
6 Tbsp of oil
1/2 medium onion, finely chopped
3 cloves garlic, peeled and finely chopped
The cooked meat (about 3 cups - note if you use more than 3 cups, you will need to increase the amounts of the other ingredients)
A molcajete (mortar and pestle)
8 peppercorns
5 whole cloves
1/2 inch stick cinnamon
3 heaping Tbsp of raisins
2 Tbsp blanched and slivered almonds
1/4 c. chopped dried apricots, chopped
2 tsp salt, or to taste
1 1/2 pounds of tomatoes, peeled and seeded
Melt the oil and cook the onion and garlic, without browning, until they are soft.
Add the meat and let it cook until it begins to brown.
Crush the spices roughly in the molcajete and add them, with the rest of the ingredients to the meat mixture. (If you don't have a molcajete, you can use the blunt end of a pestle to crush the spices in a bowl.) Cook the mixture a few moments longer.
Add chopped apricots & raisens to the mixture. Add broth at this point if the meat needs a bit of moisture.

The Chilies:
Put 6 chiles poblanos (and you MUST use this type of chili) straight into a fairly high flame or under a broiler and let the skin blister and burn. Turn the chilies from time to time so they do not get overcooked or burn right through.
Wrap the chiles in a damp cloth or plastic bag and leave them for about 20 minutes. The burned skin will then flake off very easily and the flesh will become a little more cooked in the steam. Make a slit in the side of each chili and carefully remove the seeds and veins. Be careful to leave the top of the chili, the part around the base of the stem, intact. (If the chilies are too hot - picante, let them soak in a mild vinegar and water solution for about 30 minutes.) Rinse the chilies and pat them dry.
Stuff the chilies with the picadillo until they are well filled out. Set them aside on paper towels.

The Nogada (walnut sauce)
The day before:
20 to 25 fresh walnuts, shelled
cold milk
Remove the thin papery skin from the nuts (sometimes this is totally impossible). I used Pecans as they are plentiful here in Northern Mexico. If you use pecans omit all but 1/2Tbsp. sugar.
Completely cover the walnuts or pecans with cold milk and leave them to soak overnight.
On serving day:
The soaked and drained nuts
1/4 lb queso fresco or neufchatel cheese
1 1/2 cups thick sour crema (or creme fraiche)
1 1/2 Tbsp sugar
Large pinch of cinnamon
Blend all of the ingredients in a blender until they are smooth.
To Serve
To assemble the dish, cover the chilies in the nogada sauce and sprinkle with fresh parsley leaves and pomegranate seeds.