Cook penne in boiling salted water for about 12 minutes. In the meantime peel and finely dice the onion. Cut the ham into cubes. Heat the oil in a pot and sauté the onion. Add ham, sweat briefly and dust with flour. Pour in broth and milk while stirring. Let simmer for about 5 minutes.
Break cheese into pieces. Wash the sage, dab dry and cut into fine strips, except for a little bit for garnishing. Add sage and cheese to the sauce. Season with salt and pepper. Drain penne and arrange on plates. Spread the sauce on the penne and garnish with the remaining sage