These are best fresh out of the oven with some plugra butter. I find that when baking it really is worth it to purchase a small digital scale. They shouldn't cost you more than $30 and can be found at any good cooking store or on Amazon. —sweetbelle
Sift sugar, flour, baking soda, salt and cinnamon into a bowl. Set aside.
Place eggs into a bowl. Whisk warm, melted butter into eggs in four additions. You should end up with a fluffy completely emulsified mixture. Add the buttermilk, lemon juice and lemon zest. Whisk to combine.
Add egg mixture to dry ingredients in 3 additions using a spatula.
Peel and cut apples. Place them in a food processor and process until they are small pieces, just before they become a puree. Fold into muffin batter.
Using a 2 ounce ice cream scooper portion muffin batter into baking liners in a muffin tin. Top each muffin with chopped walnuts and a sprinkling of turbinado sugar.
Place in a preheated 325 degree oven. Bake for 15 minutes and then turn, bake for another 10 minutes. Check doneness with a toothpick and continue baking if necessary.