- Combine beef, chili powder, black pepper, and 1/8 teaspoon salt in a medium bowl. Shape into 4 equal balls.
- Heat a large cast-iron skillet over high. When the pan is hot enough to release wisps of smoke, add beef balls and press down with a firm spatula to form patties.
- Place a slightly smaller skillet directly on patties. Cook until charred, about 1 minute and 30 seconds. Remove top pan, flip patties, replace top pan, and cook until charred, about 1 minute.
- Remove top pan, sprinkle patties with remaining 3/8 teaspoon salt, and top with cheese.
- Invert top pan, and cover skillet. Steam until cheese is melted, 30 to 45 seconds.
- Place patties on buns; top with sour cream, scallions, and jalapeños.