Preparation
Preheat the oven to 400 F. Coat a 12-cup muffin pan with cooking spray.
In a small bowl, mix together 2 tablespoons of the brown sugar, the pecans and cinnamon. Set aside.
In a medium bowl, whisk together both flours, the baking soda and salt.
In a large bowl, whisk the remaining 3/4 cup brown sugar and the oil until combined. Add the eggs, one at a time, whisking well after each addition. Whisk in the applesauce and vanilla. Stir in the flour mixture in two batches, alternating with the buttermilk, just until combined. Gently stir in the apple chunks.
Pour the batter into the prepared muffin pan, filling each about two thirds full, and sprinkle evenly with the pecan mixture. Tap the pan on the counter a few times to remove any air bubbles. Bake until a toothpick inserted comes out clean, about 20 minutes.
Let cool on a wire rack for 15 minutes. Run a knife round the muffins to loosen them and unmold. Enjoy warm or let cool completely before storing in an airtight container in the refrigerator for up to 3 days or in the freezer for up to 3 months.