Preheat the oven to 400°F. Liberally oil a well-seasoned 12-inch cast-iron skillet or a 12-inch round baking dish and place in the oven for a few minutes to heat. Heating the pan or dish is important, as it helps the polenta form a bottom crust.

In a heavy saucepan, whisk together the polenta and water and place over medium heat. Bring slowly to a boil, whisking often to prevent lumps from forming. Reduce the heat to low and simmer uncovered, stirring occasionally, for just a few minutes until smooth. Season with salt and black pepper and carefully pour into the hot prepared skillet or dish.

Bake the polenta cake until it pulls away from the sides of the pan and is lightly golden, 30 to 40 minutes. The cake will be crisp.

While the polenta cake is baking, prepare the spicy greens: Bring a large pot of salted water to a boil, add the greens, and boil until very tender, 15 to 20 minutes. Drain the greens into a colander, pressing firmly on them with the back of a spoon to force out excess moisture. Chop the greens coarsely. In a sauté pan, heat the olive oil over medium heat. Add the garlic and the greens and cook, stirring, until heated through and coated with the oil, about 5 minutes. Add the vinegar, red pepper flakes, and salt to taste. Remove from the heat.

When the polenta cake is ready, remove from the oven and invert onto a cutting board. Cut into wedges and divide among individual plates. Top the wedges with the warm greens, again dividing evenly, and scatter the cheese over the top. Serve immediately.

Variations:

This versatile polenta cake also can be topped with herbed cream cheese and smoked salmon, with sautéed mushrooms and shaved Parmesan cheese, or with crab, shrimp, or smoked trout salad made with mayonnaise and celery.