Baking these delightful Cinnamon Roll Muffins can easily be accomplished by following these straightforward steps:

1. Preheat the Oven: Preheat your oven to 350°F (175°C) and line a muffin tin with paper liners or grease it lightly.
2. Mix Dry Ingredients: In a large bowl, whisk together the flour, baking powder, baking soda, salt, granulated sugar, and ground cinnamon until well combined.
3. Combine Wet Ingredients: In another bowl, combine the melted butter, egg, buttermilk, and vanilla extract. Mix until smooth.
4. Combine Mixtures: Gradually add the wet ingredients to the dry ingredients, stirring gently until just combined. Be careful not to overmix; the batter should be slightly lumpy.
5. Prepare Filling: In a small bowl, mix the brown sugar and chopped nuts (if using).
6. Fill Muffin Liner: Fill each muffin liner with a tablespoon of batter. Sprinkle a small amount of the brown sugar filling over the batter, and then add another tablespoon of batter on top to cover the filling completely.
7. Make Topping: In another small bowl, mix together the sugar and cinnamon for the topping. Drizzle the melted butter over the top of each muffin and sprinkle the cinnamon-sugar mixture generously over them.
8. Bake: Place the muffin tin in the preheated oven and bake for 20-25 minutes or until a toothpick inserted in the center comes out clean.
9. Cool: Once baked, remove the muffins from the oven and let them cool in the pan for about 10 minutes before transferring them to a wire rack to cool completely.
10. Prepare Glaze (optional): If you desire a glaze, whisk together the powdered sugar, milk, and vanilla extract in a bowl until smooth, then drizzle it over the cooled muffins.

By following these steps, you can enjoy the delightful goodness of Cinnamon Roll Muffins in no time!