1. Cover potatoes with cold salted water by 1 inch in a large saucepan. Bring to a boil, then reduce heat and simmer until potatoes are just tender, about 20 minutes. Drain and cool, then cut into bite-size pieces.
2. Heat oil and 1 tablespoon butter in a well-seasoned 10-inch cast-iron skillet over high heat until foam subsides, then saute potatoes with salt and pepper to taste, turning once or twice, until nicely crusted, 8 to 10 minutes. Transfer to a serving bowl.
3. Saute corn and squash in remaining 3 tablespoons butter in skillet over moderately high heat, stirring, until crisp-tender, about 5 minutes. Stir in beans and saute, stirring, until heated through. Season with salt and pepper and add to potatoes with onion and chives, stirring to combine.

Yield: 6 servings