Preheat your oven to 350 degrees F. Brush the bottom and sides of an 8-by-8-inch casserole dish with 1 tablespoon of the melted butter.
In a large mixing bowl, whisk together the remaining 1/2 cup melted butter with the polenta, mascarpone, milk, creamed corn, whole corn, and egg. Season with salt and pepper. Pour into the prepared casserole dish and smooth the top. Bake until set, about 1 hour.