Heat the oven to 350°F/175°C. In a casserole, heat the oil and fry the bacon lardons until lightly browned and their fat is rendered. Stir in the onions, cover and cook over very low heat stirring often, until very soft and transparent, at least 20 minutes. Stir in the paprika and cook for 2 minutes longer.
Meanwhile, trim the beef and cut it in 1 ½ in/4 cm cub