Melt 1 1/2 oz. butter in a saucepan. Add the 1/4-in. sliced kidneys for 2 mins. Remove kidneys and set aside.
In a casserole wide enough to accommodate the kidneys in one layer, prepare a sauce with the remaining butter and flour. When it begins to color add the broth. Reduce for 1 minute and add kidneys and Marsala. Cook for 2 mins. on lively flame. Remove and add chopped parsley. Serve.