1. Preheat Oven and Prepare Muffin Tin: Start by preheating your oven to 375 F (190 C). Line a 12-cup muffin tin with paper liners or grease it thoroughly with butter or non-stick spray. This ensures your muffins won’t stick and makes for easy cleanup.

2. Combine Wet Ingredients: In a large mixing bowl, whisk together the active sourdough starter, 1/2 cup granulated sugar, 1/4 cup melted butter, egg, and vanilla extract until the mixture is smooth and well combined. The mixture should look slightly pale and creamy.

3. Whisk Dry Ingredients: In a separate medium bowl, combine the all-purpose flour, baking powder, baking soda, and salt. Whisk them together thoroughly to ensure the leavening agents are evenly distributed, which helps the muffins rise properly.

4. Combine Wet and Dry: Add half of the dry ingredient mixture to the wet ingredients, stirring gently until just combined. Then, pour in the milk and stir until mostly incorporated. Finally, add the remaining dry ingredients and mix until just combined. Be careful not to overmix; a few lumps are perfectly fine and help keep the muffins tender. Overmixing can lead to tough muffins.

5. Fill Muffin Cups and Bake: Divide the batter evenly among the 12 prepared muffin cups. Fill each cup about two-thirds full. Place the muffin tin in the preheated oven and bake for 18-20 minutes, or until a wooden skewer inserted into the center of a muffin comes out clean. The tops should be golden brown and spring back when lightly touched.

6. Prepare Cinnamon Sugar Coating: While the muffins are baking, prepare your coating. In a shallow bowl, combine the remaining 1/2 cup granulated sugar and 2 teaspoons ground cinnamon. In another shallow bowl, melt the remaining 1/4 cup of butter.

7. Coat the Warm Muffins: Once the muffins are baked, remove them from the oven and let them cool in the muffin tin for about 5 minutes. This allows them to firm up slightly. Then, carefully remove them from the tin. While still warm, dip each muffin first into the melted butter, ensuring it’s fully coated, then immediately roll it in the cinnamon sugar mixture until well covered. Serve warm and enjoy!