'This is with broiled foods,' writes Edward Giobbi in 'Pleasures of the Good Earth.An artist friend of mine said his father often made polenta and always made a cross on the surface before broiling.'1 cup chopped string beans, cut into 1-inch sections 4 cups loosely packed spinach 1 medium onion, coarsely chopped 1 tablespoon olive oil plus extra for sprinkling salt to taste The polenta: 1 cup fine-ground cornmeal 4 cups water 1 teaspoon table salt freshly ground black pepper Cook the string beans in salted boiling water in an uncovered pot until they are tender but firm, about four minutes. Cook the spinach in boiling water for two minutes, drain, cool, and squeeze out all excess moisture. Saute the onion in the olive oil until it begins to brown, then mix with the beans and spinach and season with salt to taste. Preheat the broiler to hot. For the polenta: Bring the water and salt to a gentle boil in a 2-quart (or larger) heavy saucepan. Add the cornmeal to the water gradually by letting it trickle from your hand in a slow, steady stream, stirring constantly with a wooden spoon in your other hand. Continue until you have used as much of the cornmeal as necessary to make a polenta that is the consistency of thick porridge. It will be almost done by the time you have added the final grains. Continue to cook about one minute. As soon as the polenta is cooked, add the vegetables and mix them in. Immediately pour the polenta and vegetable mixture into a 10-inch pie plate. Smooth the surface with a spatula and sprinkle with olive oil and pepper. Place under the broiler until its surface is lightly charred. Serves 6.