Preheat the broiler. Remove the skillet and the parchment and broil the cake 8 inches from the heat for about 10 minutes, rotating the dish to evenly brown and crisp the vegetables. Let stand for 15 minutes. Cover the baking dish with a flat cookie sheet and, using oven mitts, carefully invert the cake onto the cookie sheet. Remove the baking dish and parchment paper. Brush the cake with melted butter and season with salt.