Mince the beef. Peel the onion, rinse it and slice it finely. Heat the oil and butter in a saucepan add the onion and fry it until soft but not golden, add the minced meat and brown it; mix the mince and brown it over a high heat until evenly golden and stirring with a wooden spoon; add the kernels and after a few minutes ladle some broth over it; cover and simmer over a medium heat for about 45 minutes.Flavour with a pinch of salt and a grind of pepper. Peel the garlic and slice it finely, add the yoghurt and stir well. In the meanwhile cook the pasta in plenty of boiling water. Drain it al dente and season it with the yoghurt, the garlic and half of the sauce. Pour it in a heated serving dish, sprinkle it well with the remaining condiment and serve immediately.