Steak Nicola

• 1 shallot (chopped)
• 1 potatoes noisettes to decorate
• 1/2 onion (chopped)
• 1/4 dry port
• 240 gr creme fraiche
• 130 gr fillet mignon steaks
• 120 ml beef broth
• 55 gr butter
• 40 gr mushrooms (sliced)
• 20 ml olive oil