In a large, heavy skillet heat olive oil and butter over medium-high heat. Add medallions and cook for 5 minutes, or until nicely browned. Turn and cook for 5 more minutes. Remove medallions from pan and keep warm.
Add garlic and mushrooms to skillet and saute for 5 minutes. Return medallions to pan and pour in broth. Reduce heat to medium and cook, uncovered for 15 minutes, or until liquid has almost evaporated. Serve.