Ukrainian Beef Strogonov

• 1,400 gr filet mignon tips
• 250 gr mushrooms
• 180 ml sour cream
• 160 ml cream (heavy)
• 120 gr onion (finely chopped)
• 34 gr butter (unsalted)
• 12 ml dijon mustard
• 9 gr dill (fresh)
• 7 gr flour
• 2 gr parsley (fresh)