Preheat the oven to 120 degrees and warm a plate with it.
Finely chop the tarragon.
Season the steaks with salt and pepper. Fry in the very hot clarified butter on the first side for 2 minutes, on the second side, depending on the thickness, only 1-1 1/2 minutes. Immediately place in the preheated dish and cook in the 120 degree oven for 8-10 minutes.
Dissolve the roast set with cognac and white wine and reduce to 1/2 dl. Pour in the cream, stir in the mustard and only let the sauce cook until it thickens. Finally add the tarragon and season the sauce with sugar, salt and pepper.