Preheat your oven to 180°C (350°F) and lightly grease a muffin tin to prevent sticking.
In a large mixing bowl, whisk together the flour, granulated sugar, baking powder, and salt until evenly combined. This creates a light, airy dry base.
In a separate bowl, melt the butter and then whisk in the milk and vanilla extract until smooth. The mixture should be fragrant and slightly warm.
Pour the wet ingredients into the dry mixture and gently fold with a spatula until just combined. The batter will be thick and slightly lumpy—avoid overmixing to keep the muffins tender.
In a small bowl, combine the cinnamon and sugar to make the cinnamon sugar topping. Mix well and set aside.
Spoon the batter into the prepared muffin tin, filling each cup about two-thirds full. Use a spoon or scoop for even portions.
Sprinkle a teaspoon of the cinnamon sugar mixture on top of each muffin before baking. Press gently to help it stick to the batter.
Bake in the preheated oven for 20–25 minutes, until the tops are golden brown and crackly, and a toothpick inserted into the center comes out clean.
Remove the muffins from the oven and let them rest for about 5 minutes in the tin. Then transfer them to a wire rack to cool slightly or serve warm.
Enjoy these warm, crackly-topped cinnamon sugar muffins with a cup of coffee or tea for a cozy treat.