Preheat the oven to 350 F (180 C) and prepare a muffin tin with 12 paper liners.In a bowl, combine the flour, sugar, baking soda, baking powder, salt, and nutmeg. Set aside.In another bowl, mix the buttermilk, rum, oil, apple cider vinegar, and vanilla seeds.Combine the wet ingredients with the dry ingredients, mixing gently with a spatula.Divide the batter among the prepared molds and bake for 20 to 25 minutes or until a toothpick inserted into the center comes out clean.Let cool for 5 minutes in the mold before transferring to a wire rack to cool completely.Glaze:Beat the butter with an electric mixer, then add the powdered sugar, buttermilk, and rum.Beat until smooth and creamy.Put the mixture into a pastry bag fitted with a fluted tip and frost the cupcakes.Sprinkle the cupcakes with ground cinnamon and enjoy.