Trim and wash turnips and radishes. Slice them. If you need to, cut some slices so that all pieces are roughly the same size.

Heat butter or oil in a saute pan. Add the vegetables, stir to distribute the butter.

Cook, stirring every minute or two, for five minutes. Check to see if done. If not yet, you can give them another minute or two, or turn off the heat, cover the pan, and let it cook in its own steam.

Serve at once.