First, prep the pablano and jalapeno peppers by roasting them over an open flame on the stove, turning until blackened on all sides. If you do not have a gas oven, put the peppers on a sheet pan in the broiler of the oven, turning once to ensure both sides blacken nicely.
Once the peppers are warm enough to handle, dice the jalapeno and set aside. Then remove the skin and seeds of the pablano pepper and dice and set aside as well.
Preheat the oven to 325 degrees.
Get a dutch oven on the stove over high heat and add the bacon fat.
Salt and pepper the steak liberally and sear in the dutch oven until browned on both sides. Remove the steak and set aside.
Add the diced onion and minced garlic to the same dutch oven over medium heat and cook until the onion is just starting to become tender, about 5-7 minutes.
Pour in the one bottle of modelo and just enough beef stock to nearly cover the meat. This will vary depending on the size pot you are using, so you can use more of the modelo or beef stock to get you there depending on your preference. As you pour in the liquid, scrape up the delicious bits in the bottom from searing the steak and cooking the onions.
Add the peppers, the chili powder, cumin, cilantro stems, and lime cut in half, stir until spices well mixed.
Put a lid on the dish and pop in the oven to cook for 3 hours.
Remove from the oven and remove the lid. Remove the beef from the liquid and set aside. Strain the braising liquid and discard the solids.
Add 1/4 cup of the braising liquid and 2 tbs of butter to the beef, and shred with two forks.
Serve on warm flour tortillas and top with whatever you like.