Step 1: Make the polenta: In a medium nonreactive saucepan, bring the broth, salt and pepper to a boil over high heat. Gradually whisk in the polenta. Cook until bubbling and thick, 5 to 8 minutes, stirring with a wooden spoon. Stir in the 3 tablespoons of butter and the Parmesan.
Step 2: Transfer the hot polenta to a buttered baking dish and smooth the top with a spatula. Let cool completely, then cover with foil or plastic wrap and refrigerate overnight.