In a medium sauce pan, saute the onion and garlic in the oil over medium-high heat, until tender (about 3 minutes).

Stir in the flour, cumin, salt and pepper and cook over medium heat, stirring, for 2 minutes.

Stir in the stock and simmer until thick and smooth.

Puree a small amount of chiles and add to sauce

Chop remaining green chiles to desired consistency and add to sauce

Add tomatoes and pork and additional stock to desired consistancy.

Saute for 15 to 20 minutes