Preheat your oven to 350°F (175°C) and grease a muffin tin or line it with paper liners.
In a large mixing bowl, combine the all-purpose flour, granulated sugar, baking powder, baking soda, salt, and ground cinnamon. Whisk together until well blended.
In another bowl, mix the melted butter, milk, eggs, and vanilla extract until combined.
Pour the wet ingredients into the dry ingredients. Using a rubber spatula, gently fold the mixture until just combined. Be careful not to overmix; a few lumps are fine.
Spoon the batter into the prepared muffin tin, filling each cup about two-thirds full.
In a small bowl, mix together the brown sugar and a pinch of cinnamon. Sprinkle this mixture evenly over the tops of the muffins.
Bake in the preheated oven for 18-20 minutes, or until the muffins are golden brown and a toothpick inserted into the center comes out clean.
Allow the muffins to cool in the tin for about 5 minutes before transferring them to a cooling rack to cool completely.