1. Feed starter or stir discard to reincorporate liquid

2. Preheat oven to 350°F and grease or line a 9×5-inch loaf pan

3. Peel, core, and dice apples, toss with 1 teaspoon cinnamon and set aside

4. Whisk melted butter, brown sugar, eggs, and vanilla until creamy

5. Stir in sourdough starter until combined

6. In a separate bowl, mix flour, baking powder, remaining cinnamon, and salt

7. Fold dry ingredients into wet mixture until just combined

8. Gently fold in diced apples

9. Combine crumb topping ingredients with a pastry cutter until crumbly

10. Pour batter into prepared pan and sprinkle crumb topping evenly

11. Bake until golden brown and a skewer comes out clean, about 50 minutes

12. Cool in pan 10 minutes then transfer to a wire rack

13. Store at room temperature up to three days or freeze slices for longer storage