Preheat the oven to 375°F (190°C) and prepare a muffin tin with liners or grease.
In a large bowl, mix the dry ingredients: flour, sugar, salt, baking powder, cinnamon, and nutmeg. Set aside.
210 g All-purpose or whole wheat flour or 50/50, 100 g Cane sugar, ½ tsp Salt, 1 tsp Baking powder, 1 ½ tsp Cinnamon, ½ tsp Nutmeg
In a small bowl, mix the sourdough discard with the baking soda. Let it sit for a minute until it bubbles slightly.
140 g Sourdough discard, 1 tsp Baking soda
In a separate bowl, combine the melted butter, sour cream, milk, vanilla, and the activated sourdough discard. Stir until smooth.
120 ml Melted butter or coconut oil, 120 g Sour cream, 60 ml Milk, 1 tsp Vanilla extract
Gently fold the wet ingredients into the dry ingredients, stirring just until combined. Be careful not to overmix.
Fold in the diced apples until evenly distributed.
1 Apple
Scoop the batter into the muffin tin, filling each cup about ¾ full.
For the topping (optional), mix sugar and cinnamon in a small bowl, then sprinkle over each muffin. Add nuts or oats if using.
Bake for 18–22 minutes, or until a toothpick inserted into the center comes out clean.
Let the muffins cool in the pan for 5 minutes, then transfer to a cooling rack to cool completely.