Heat 1 tablespoon oil in a large cast-iron skillet over medium-high heat. Add beef, cumin, salt and pepper; cook, stirring often to break up the meat. Continue for about 6 minutes or until evenly browned. Using a slotted spoon, transfer the beef to a paper-towel-lined plate; do not wipe out the pan. Add 1 tablespoon oil to the drippings in the pan. Add potatoes; cook, stirring occasionally. Continue for about 20 minutes or until potatoes begin to caramelize and become tender. Transfer the potatoes to the plate with the beef.