Brown the cubed beef in the fat on medium heat in a large Dutch oven or pot (may have to do in batches). Add the onions, garlic, tomatillos, jalapenos, cumin, 1/2 cup of the chopped cilantro, four cups of water (or beer if you prefer), salt and pepper to taste.
Bring to a boil and then lower to a simmer and cook for two hours until meat is tender. Remove beef from the pot, shred it and then toss it with the lime juice and some salt and black pepper. Can also add some of the pan juices if you like. Otherwise, you can reserve the pan juices for another use.
Wrap the tortillas in foil, and heat in a 350-degree oven for 10 minutes or until soft. Take each warmed tortilla and place two tablespoons of the shredded beef into it and roll tightly.
Heat the canola oil in a large iron skillet and when oil is 350 degrees (or hot but not smoking), gently place three flautas into oil, seam side down, and cook on each side until crisp, 45 seconds per side.
Serve immediately with salsa, chopped cilantro, onion and sour cream.