Heat 1 tablespoon olive oil in a large Dutch oven over medium-high heat. Add half of the beef and cook, stirring, until browned, about 4 minutes; transfer to a plate. Add the remaining 1 tablespoon olive oil to the pot and brown the remaining beef, then return the first batch to the pot. Reduce the heat to medium and stir in the garlic.
Combine the chili powder, cumin and flour in a small bowl. Sprinkle over the meat in the pot and stir until evenly coated. Crumble in the oregano with your fingers, then add 3 cans beef broth, 2 teaspoons salt and 1/4 teaspoon pepper; stir to combine. Bring to a boil, then reduce the heat to low; partially cover and simmer until the meat is just tender, about 1 hour, 30 minutes.
Whisk the remaining 1 can broth with the masa harina in a bowl to make a creamy paste; stir into the chili. Continue simmering over low heat until the meat is almost falling apart, 30 minutes to 1 hour, adding up to 2 cups water if the chili gets too thick. Divide among bowls and top with onion and pickled jalapenos.