In a heavy saucepan, combine the ingredients and warm over low heat. When small bubbles appear around the sides of the pan, remove it from the heat and let the mixture sit at room temperature for 15 to 20 minutes. Place the pan back on the stove and rewarm the mixture, whisking it briefly to redistribute the skin that forms on the milk's surface. Remove the vanilla bean half, scrape out the seeds with a sharp knife, and return the seeds to the milk. Pour the vanilla milk into mugs and sprinkle cinnamon on top. Serve warm.