In a large mixing bowl, cream together the softened butter and sugar.
Add the sourdough starter, applesauce, and maple syrup. Mix until combined.
Stir in the flour, oats, and salt.
Cover with a tea towel and allow the batter to sit in a warm place to ferment for 8-24 hours. This step is optional. For a quick recipe that doesn’t require fermentation, you can follow the remaining steps right away.
Once the batter has fermented, preheat the oven to 350 °F.
In a small bowl or measuring cup, prepare a chia egg by mixing together 1 tbsp of chia seeds with 3 tbsp of warm water. Let this mixture sit for 5 minutes to thicken.
Wash, peel, and dice one apple to be set aside.
Uncover the fermented batter and add the vanilla extract, chia egg, baking soda, baking powder, cinnamon, and salt. Mix until combined.
Fold in the diced apples and chopped pecans with the fermented batter.
Lightly coat a muffin pan with olive oil or fit with paper liners.
Generously fill the coated or lined muffin tins with batter, about 3/4 full. Optionally, top the muffins with additional chopped pecans.
Bake full sized muffins for 20-25 minutes at 350 °F. Bake mini muffins for 15-20 minutes at 350 °F.
Once completely cool, transfer the muffins to an airtight container. Enjoy within 3 days when stored at room temperature, within 1 week when stored in the refrigerator, or freeze to enjoy within 3 months.