Preheat the oven to 425°F. Line a 12-count muffin pan with cupcake liners or spray with nonstick spray. The recipe makes 15-16 muffins, so prepare a second muffin pan in the same way.
In a large bowl, shift together the flour, baking soda, cinnamon, and salt. Set aside. In a medium bowl, whisk the eggs, maple syrup, yogurt, applesauce, milk, and vanilla together until combined. Pour the wet ingredients into the dry ingredients, stir a few times, then add the grated apple and walnuts. Fold everything together gently until just combined and no flour pockets remain. Avoid overmixing— whole wheat flour is more dense so to keep it lighter we not only sift it but also need to be more gentle with the batter.
Spoon the batter into the liners, fulling them all the way to the top. Bake for 5 minutes at 425°F then, keeping the muffins in the oven, reduce the oven to 350°F. Bake for an additional 13-15 minutes or until a toothpick inserted into the center comes out clean. The total time for the muffins is about 18-20 minutes. Allow the muffins to cool for 5 minutes in the muffin pan, then transfer to a wire rack to continue finish cooling.
Muffins stay fresh covered at room temperature for up to 3 days, then transfer to the refrigerator for up to 1 week.
Make ahead tip: The muffins can be frozen for up to 3 months. Allow to thaw overnight in the refrigerator, then bring to room temperature or warm up in the microwave if desired.1. Any fat % of yogurt can be used for these. To make this dairy-free, use dairy-free yogurt. I prefer using Kite Hill plain unsweetened since it has a plain flavor.2. Any milk fat % or dairy-free milk can be used— I typically use unsweetened almond milk.3. Avoid overmixing— whole wheat flour is a more dense flour so to keep it lighter we will not only sift it but also need to be more gentle with the batter to keep air in it.4. Use any variety of apple that you prefer. However, if using a sweeter apple, you may need to reduce the maple syrup slightly.Make these vegan: Use 1 chia seed eggs (1 chia seed egg = 1 Tablespoon chia seeds + 2.5 Tablespoons water + let sit for 5 minutes) with dairy-free yogurt, and any dairy-free milk.