Clean the mushrooms and cut into slices. Peel the onion, dice finely. Rinse the fillet, pat dry, cut into 1 cm thick slices. Rinse the chives, cut into rolls.
Heat the clarified butter in a saucepan or high pan. Season the fillets with salt, pepper and paprika, fry on both sides and remove from the pan.
Place the mushrooms and onions in the frying fat, fry briefly. Deglaze with the stock and cream. Add the medallions and lemon zest and simmer for 5 minutes.
Heat the spaetzle in butter according to the instructions on the package. Season the fillet pot with salt and pepper. Stir in chives and serve with spaetzle.