1. 1. Prepare Your Oven and Muffin Tin: Preheat 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 prevents sticking and makes for easy cleanup.

2. 2. Combine Wet Ingredients: In a large mixing bowl, whisk together the active sourdough starter, granulated sugar, melted and cooled butter, large egg, and vanilla extract until well combined and smooth. The mixture should be slightly thick and creamy.

3. 3. Whisk Dry Ingredients: In a separate medium bowl, combine the all-purpose flour, baking powder, baking soda, and salt. Whisk these dry ingredients together thoroughly to ensure they are evenly distributed. This step is crucial for even leavening.

4. 4. Combine Wet and Dry Mixtures: Add the dry ingredients to the wet ingredients. Using a spatula or wooden spoon, gently mix until just combined. Be careful not to overmix; a few lumps are perfectly fine. Overmixing can lead to tough muffins.

5. 5. Fold in Strawberries: Gently fold in the diced fresh strawberries. Distribute them evenly throughout the batter without crushing them too much.

6. 6. Fill Muffin Cups: Divide the batter evenly among the 12 prepared muffin cups. Each cup should be about two-thirds full. If desired, sprinkle the tops of the muffins with turbinado sugar for a lovely crunchy topping.

7. 7. Bake Until Golden: Bake for 20-25 minutes, or until the muffins are golden brown and a wooden skewer or toothpick inserted into the center of a muffin comes out clean. The tops should spring back when lightly touched.

8. 8. Cool and Serve: 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. This helps prevent them from becoming soggy on the bottom.