Pre-heat your oven to 350F.
Slice the onion into 3/4 inch slices.
Peel the garlic.
Place the onion and garlic in a dry comal or cast iron frying pan and cook until the garlic and onion brown. Watch the garlic closely.
Coarsely chop the onion and combine it with the chili powder, mexican oregano if using and 2 1/2 cups chicken stock in a blender. Puree completely. Set aside.
In a high sided pot large enough hold all the pork melt two Tbsp of lard or vegetable oil and brown the meat in batches. Brown it thoroughly. Take the time. It's worth it.
Remove meat from the pan and add a third Tbsp of lard or oil. Transfer the chili mixture to the pan and fry, stirring constantly for 4-5 minutes. The mix will bump so don't wear nice clothes when you make this.
When the oil starts to separate (or after 5 minutes) return the pork to the pot and add enough chicken stock to cover the pork - about another 1 1/2 cups. Stir thoroughly.
Add a tsp of salt and bring to a simmer on the stove.
Cover and place the preheated oven.
Start testing for tenderness after the first hour. It will likely take around 90 minutes but results vary. You are done when the pork is tender.
Serve with pinto beans, tortillas and garnishes of your choice.