1. 1. Prepare your muffin tin: Preheat your oven to 375 F (190 C). Line a 12-cup muffin tin with paper liners or lightly grease and flour each cup. This ensures your muffins won’t stick and makes for easy cleanup.

2. 2. Combine dry ingredients: In a large mixing bowl, whisk together the all-purpose flour, 1/2 cup granulated sugar, baking powder, baking soda, and salt. Make sure there are no lumps and the ingredients are evenly distributed.

3. 3. Mix wet ingredients: In a separate medium bowl, lightly beat the large egg. Then, whisk in the milk, unfed sourdough starter, 1/4 cup melted butter, and vanilla extract until well combined.

4. 4. Combine wet and dry mixtures: Pour the wet ingredient mixture into the dry ingredient mixture. Stir gently with a spatula or wooden spoon until just combined. Be careful not to overmix; a few lumps are perfectly fine and will result in a more tender muffin. Overmixing can lead to tough muffins.

5. 5. Fill muffin cups and prepare topping: Divide the batter evenly among the 12 prepared muffin cups, filling each about two-thirds full. In a small bowl, combine the remaining 2 tablespoons of granulated sugar and 1 teaspoon of ground cinnamon.

6. 6. Add the cinnamon sugar topping: Melt the remaining 2 tablespoons of butter. Brush the tops of the unbaked muffins with the melted butter, then generously sprinkle the cinnamon sugar mixture over each muffin. This creates a beautiful, sweet, and slightly crispy crust.

7. 7. Bake the muffins: Place the muffin tin in the preheated oven and bake for 20-25 minutes, or until a wooden skewer or toothpick inserted into the center of a muffin comes out clean. The tops should be golden brown and the cinnamon sugar should be slightly caramelized.

8. 8. Cool and serve: Once baked, remove the muffin tin from the oven and let the muffins cool in the tin for 5 minutes before transferring them to a wire rack to cool completely. Serve warm for the best flavor and texture.