Sauteed Radishes and Watercress

Heat butter with oil in a 12-inch heavy skillet over moderately high heat until foam subsides, then sauté radishes with salt and pepper, stirring occasionally, 6 minutes. Add water and cook, covered, until crisp-tender, about 2 minutes, then cook, uncovered, stirring occasionally, until liquid is evaporated, 1 to 4 minutes. Add watercress and sauté, stirring, until wilted, about 1 minute.