Prepare 3 flat containers (plates or baking sheets) in order to bread the schnitzel. Put the flour and a pinch of salt and pepper in the first container. In the second container, whisk together the eggs, sour cream, nutmeg, mace, pinch salt and pepper. In the third, combine the panko breadcrumbs and grated parmesan cheese.
Dip a schnitzel in the flour and shake off all the excess. Then dip it into the egg mixture, drain excess. Lay it in the third container with the panko mixture, and bread both sides. Shake off the excess of breadcrumbs and put in a plate. Repeat with the rest of the schnitzel. Rest the breaded schnitzel in the refrigerator for one hour until dry.
Heat the oil in a large frying pan over medium heat. Cook the schnitzel around 3 minutes each size, until golden brown. Transfer to a plated lined with paper towels and season with salt and pepper.
Serve the schnitzel with mushroom sauce (recipe below).
Melt the unsalted butter in a pan and brown the onions and the mushroom. Deglaze the pan with the white wine. Reduce by one half. Add the rosemary and the veal stock. Reduce again by half again, and seasoning.