Peel the onions and cut into thin rings or slice. Briefly brown the minute steaks in hot oil and keep warm.
Put the butter in the used pan and fry the onions until translucent. Dust the flour over it and stir-fry for another two minutes. Gradually stir in the meat stock and milk. Season to taste with salt, pepper and sugar. Simmer for another 15 minutes in the open pan while stirring.
Five minutes before the end, add the steaks to the sauce and let them steep.