Preheat oven to 425°F. Grease 12 count muffin tin with melted butter or coconut oil. If you have muffin cups, you can line your muffin tin instead.
Prepare your Homemade Buttermilk. In a glass measuring cup, add lemon juice. Then, pour milk to meet the 1 cup line. Stir well and set aside until ready to use.
Prepare your Crumble Topping. In a small mixing bowl, whisk together dry ingredients for your Crumb Topping, all-purpose flour, brown sugar, granulated sugar, ground cinnamon and salt. - Drizzle melted butter over the dry ingredients and mix together until well combined and crumbles appear.
Mix and bake your Muffins. In a large mixing bowl, whisk together these Muffin ingredients: light brown sugar, granulated sugar, coconut oil, buttermilk, eggs and vanilla extract. Then, with a silicone spatula or wooden spoon, stir all-purpose flour, baking powder, ground cinnamon and salt into the wet mixture. Fold in chopped apples and chopped pecans. Evenly divide muffin mixture among 12 muffin cups. Distribute the crumble topping onto muffins, equally. Bake muffins on the center rack for 5 minutes at 425°F then without opening the door, turn down the oven temperature to 375°F and bake muffins for 15 - 17 minutes.
Cool and store. Let your muffins cool a bit on a cooling racking for 5 - 10 minutes. Muffins are best enjoyed when warm. Store at room temperature, in an airtight container, for up to 3 days.