In a Dutch oven, sear the pork strips in hot lard. With a slotted spoon, remove the pork and discard the grease. Saute the onions with a little salt in fresh lard until soft. Add the jalapeno peppers and saute for a few minutes. Return the pork to the pot.
Sprinkle in the flour. Stir to combine. Stir in the ground chiles and cumin. Throw in the garlic and tomatoes. Add enough beef stock to cover the mixture. Season to taste with salt and pepper. Stir the pot until the ingredients are well-incorporated. Bring the liquids to a hard-boil, cover, cut the heat to a slow simmer and braise for 1 1/2 - 2 hours. Stir the pot - on occasion. Serve the Carne Guisada in small bowls with flour tortillas on the side.