Sprinkle 2 teaspoons of salt evenly over the cubed beef chuck and set aside for at least an hour.
Preheat a dry cast-iron comal or pan over medium-high heat. Toast the chiles on each side for 2-3 seconds by pressing them onto the comal with a metal spatula (being careful not to burn them). Add to a pot of simmering water and soak for 20 minutes.
Preheat a cast iron dutch oven over medium heat and add the reserved beef fat. Render until at least 2 tablespoons of liquid is released. Throw away the solids.
Increase the heat on the dutch oven to high and add one-half of the cubed beef. Cook undisturbed until the meat no longer sticks to the cooking surface and has browned (not grayed) on one side. 3-4 minutes. Flip and cook the other side until it has also browned nicely. Remove and set aside. Brown the other half of the beef, remove and set aside.
Reduce heat to medium high, add 2 tablespoons of cooking oil. Add the diced onion, jalapenos, and a pinch of salt. Cook, stirring, 10 minutes, until the onion is translucent and starting to brown. If the onion begins to stick, deglaze with 1/4 cup of chicken stock, then reduce until its almost dry again. Add the tomato paste, cumin, cayenne, oregano, and cook, stirring constantly, an additional 1 minute.
While the onions are cooking, drain the chiles very well and transfer them to a blender jar, along with 1 1/2 cups of chicken stock, and the garlic. Blend on high speed until very smooth.
Add the chile puree, the diced tomatoes, beer, and Sazon Goya to the dutch oven and stir very well. Bring to boil, then reduce to a simmer. Cover and cook for an additional 2 1/2 hours.
Remove the lid to the dutch oven, increase the heat to medium, and reduce the liquid until it is starting to thicken. 15-20 minutes.
Sprinkle the masa harina all over the top of the chili, then thoroughly stir it in. Cook an additional 10 minutes, then stir thoroughly again, breaking up any masa clumps you find. Serve.