Preheat your Dutch oven over medium-high heat and add the beef tallow. Once the beef tallow is melted and beginning to smoke, add the ground beef and press down firmly with a sturdy spatula. Let sear undisturbed for a least a minute, then break it up with your spatula and brown it the rest of the way. Remove the browned beef with a slotted spoon and pour off all but 2 tbsp. of the remaining oil.
Add the onion, poblano, and jalapenos, Cook, stirring often, until the poblano and jalapenos are soft, and the onions are starting to become translucent. Add the garlic, chili powder, cumin, oregano, salt, and black pepper, and cook an additional minute.
Add the ground beef, diced tomatoes, tomato paste, beer, and beef stock. Reduce heat to low, cover and simmer for 2 hours, stirring on occasion.
Spoon off any oil that has risen to the top, then increase heat to medium-low, and simmer for 1/2 an hour, stirring occasionally. Taste for salt and pepper, and adjust.