Create the marinade by combining all its ingredients in a medium saucepan and bringing it to a low simmer. Allow to simmer for half an hour, then let it cool. Put it in the fridge to get cold.
Lightly salt the goose legs on all sides. Once the marinade is cold, add the goose legs to the marinade. If you plan to use a sous vide, seal the marinade with legs in a bag and sous vide at 170 F for 14 hours. If not using a sous vide, marinate the legs overnight.
In a large skillet, heat on medium-low, add the finely minced onion and lightly salt it. Stir it until seared and caramelized, approximately 20-30 minutes. Add the enchilada sauce, beef stock, ale, morello cherry preserves, paprika, granulated garlic, cumin, coriander, and chili powder. Stir the ingredients and turn heat to low.
Add the goose legs to the skillet and cover. If the legs were sous-vide cooked ahead of time, this process won’t take as long (perhaps 1-2 hours). At the 1-hour mark, you may wish to cut meat off the bone into chunks and add back to the skillet for another hour. If the legs were not sous-vide cooked ahead of time, this process could take upwards of 6 hours or longer, during which you will likely need to add enchilada sauce, beef stock, and ale into the skillet to keep it from drying out.