Preparation Pour warm polenta into a large ovenproof skillet or a ceramic baking dish or metal baking pan and spread into an even layer (ideally about 1” thick). Let cool, then cover and chill at least 1 hour and up to 1 week. Preheat oven to 500°F. Heat garlic and ¼ cup oil in a large skillet over medium, stirring occasionally, until garlic is fragrant and starting to brown, about 3 minutes. Add beans and red pepper flakes (if using), then, working in batches, add kale, letting it wilt slightly after each addition before adding more, and cook, stirring occasionally, until tender and evenly darkened in color, about 3 minutes. Stir in vinegar and salt and cook, still stirring occasionally, until liquid evaporates, about 2 minutes. Remove from heat and stir in ¼ cup Parmesan. Scrape kale mixture over prepared polenta and spread into an even layer. Drizzle with more oil and sprinkle with more Parmesan. Transfer skillet to oven and bake until polenta is warmed through and topping is lightly crisped and browned, 8–10 minutes.