How to Make It
Preheat oven to 350°. Lightly coat a 9x5-inch loaf pan with cooking spray; line the pan with parchment paper, leaving 1-2 inches to hang over the sides of the pan.
Whisk together the flour, baking soda, and salt in a medium bowl; set aside.
Stir together the brown sugar, cinnamon, and pecans (if using) in another bowl; using a fork, work 2 tablespoons of the softened butter into the brown sugar mixture. Stir the chopped apple into the mixture to combine and coat.
In a large bowl, beat the remaining ½ cup butter and granulated sugar with an electric mixer at medium-high speed until pale and fluffy, 4-5 minutes. Add the eggs and vanilla; mix until just combined. Mix in about half of the flour mixture. Mix in the sour cream, followed by the remaining flour mixture, mixing until just combined.
Pour half of the batter into the prepared pan. Spoon a little more than half of the apple mixture over the batter, lightly pressing the apples in. Top the apples with the remaining batter. Spoon the remaining apple mixture over the top of the loaf, lightly pressing in. Bake at 350° for 55-57 minutes or until a wooden skewer inserted into the center of the loaf tests clean. Cool completely in the pan. To serve, lift the loaf from the pan using the parchment overhang and slice.