Pound The Steaks Out To 1/2 Inch Thickness. Coat Steaks Lightly With Flour Seasoned With Salt And Pepper. Dip Steaks Into Lightly-Beaten Eggs, Then Coat With Combined Breadcrumbs And Parsley, Pressing On Firmly. Place Steaks On To Tray, And Refrigerate Until Ready To Cook. In A Large Frying Pan, Heat 1/4 Cup Butter And Oil Over Medium-High Heat. Cook Steaks Until Golden Brown, And Cooked To Desired Doneness. Remove From Pan, And Keep Warm. In A Metal Bowl, Whisk Together Egg Yolks, Lemon Juice, Salt, Pepper, And Mustard. Place The Bowl Over Simmering Water, And Stir Until Sauce Is Thick And Creamy. Whisk In The Remaining 1/2 Cup Softened Butter, And Remove From Heat. Place Steaks Onto Serving Plates, Place Two Slices Of Avocado On Each Steak, And Spoon The Mustard Sauce Over Each One.