Cut the meat fillet into strips of equal size, a finger thick and about 3 cm or 1 inch long.
Clean the mushrooms with water and cut it into small slices.
In a mortar, crush the garlic with the peppercorns and salt. Marinate the meat with this mixture and leave to sit for about 20 minutes (optional).
In a very hot pan, add olive oil in and saute the meat until golden brown. Add onion in and stir it around until cooked. By doing this, we seal it and make the meat tender inside.
Add bone broth, mustard and sour cream. Stir gently and simmer with the lid on for about 15 minutes.
Finally, add sliced mushrooms and the pickles. Mix well and cook a couple of minutes to achieve the desired texture and flavor.
Remove from heat. Top with tarragon and parsley. You can accompany this dish with cauliflower rice or zucchini pasta.