Creating these delectable Cinnamon Swirl Muffins is simple if you follow these steps:

1. Preheat the Oven: Preheat your oven to 350°F (175°C) and line a muffin tin with paper liners or grease it well.
2. Mix Dry Ingredients: In a large bowl, whisk together the flour, granulated sugar, baking powder, salt, and ground cinnamon.
3. Combine Wet Ingredients: In another bowl, mix the melted butter, milk, eggs, and vanilla extract until well combined.
4. Combine Mixtures: Pour the wet ingredients into the dry ingredients and stir until just combined. Be careful not to overmix; a few lumps are okay.
5. Prepare the Swirl: In a small bowl, combine the brown sugar and cinnamon for the swirl mixture.
6. Fill Muffin Tins: Divide half of the muffin batter evenly among the muffin cups. Sprinkle half of the cinnamon-sugar mixture over the batter.
7. Add Remaining Batter: Spoon the remaining muffin batter over the cinnamon-sugar layer, filling each cup about ¾ full. Top with the remaining cinnamon-sugar mixture.
8. Bake: Place the muffin tin in the preheated oven and bake for 20-25 minutes or until a toothpick inserted into the center comes out clean.
9. Cool: Remove the muffins from the oven and allow them to cool in the tin for 10 minutes before transferring them to a wire rack to cool completely.

These steps will guide you in creating a batch of incredible Cinnamon Swirl Muffins effortlessly!