In a medium saucepan, over medium-low heat, the heat the oil with the garlic, and cook until softened, about 3 minutes. Add the pepper flakes and cook for 30 seconds more. Add the broth and milk, and bring to a boil over high heat. While whisking constantly, slowly pour the cornmeal into the hot liquid. Stir in the salt. Lower the heat to cook the mixture at a gentle simmer. Cook, stirring frequently, until the cornmeal is creamy and not all grainy, about 30 minutes. Remove the polenta from the heat and stir the cheese, butter, and the herbs. Serve.