Preheat oven to 350. Spread 1/2 cup of the chopped pecans in a single layer on a large baking sheet. Place in oven and toast for 5-6 minutes, or until fragrant, stirring halfway through to prevent scorching. Set pecans aside.

Beat together the sour cream and next 3 ingredients at low speed just until blended. In a medium bowl, combine the flour and next 4 ingredients, whisking to blend. Add to the sour cream mixture in 3 additions, stirring just to combine after each addition. Stir in chopped apple and 1/2 cup toasted pecans.

Spoon batter into a greased 9x5-inch loaf pan. Sprinkle with the remaining 1 cup chopped pecans, and press the pecans gently into the batter.

Bake at 350 for approximately 1 hour, or until a wooden pick inserted in the center comes out clean. Shield the loaf with aluminum foil for the final 15 minutes of baking to prevent over-browning. Cool in pan on wire rack for 10 minutes. Remove from pan and place on wire rack.

Combine butter and brown sugar in a microwave-safe bowl. Cook on high for about 3 minutes, stirring after each minute of cooking, until the sugar is melted. Spoon the mixture over the loaf and allow to cool completely.