1. 1. Prepare the wet ingredients: In a large mixing bowl, combine the active sourdough starter, warm milk, melted butter, egg, granulated sugar (or sugar substitute), and vanilla extract. Whisk everything together until it’s well combined and smooth. The mixture should look slightly frothy from the starter.

2. 2. Combine the dry ingredients: In a separate medium bowl, whisk together the all-purpose flour, baking powder, baking soda, salt, and ground cinnamon. Make sure there are no lumps and the spices are evenly distributed.

3. 3. Mix wet and dry ingredients: Gradually add the dry ingredient mixture to the wet ingredients, stirring with a wooden spoon or spatula until just combined. Be careful not to overmix; a few lumps are perfectly fine. Overmixing can lead to a tough bread.

4. 4. Fold in the apples: Gently fold in the finely diced apples until they are evenly distributed throughout the batter.

5. 5. Prepare for baking: Grease and flour a 9×5-inch loaf pan, or line it with parchment paper for easy removal. Pour the batter into the prepared loaf pan, spreading it evenly.

6. 6. Bake the bread: Preheat your oven to 350 F (175 C). Bake for 45-50 minutes, or until a wooden skewer or toothpick inserted into the center of the loaf comes out clean. The top should be golden brown and firm to the touch.

7. 7. Cool before slicing: Once baked, remove the loaf pan from the oven and let it cool in the pan for about 10-15 minutes before carefully transferring it to a wire rack to cool completely. Slicing while hot can make the bread crumbly.