Prep: Preheat oven to 325°F (165°C). Grease and flour a 10-inch Bundt pan.
Dry Ingredients: Whisk flour, baking powder, baking soda, and salt in a bowl. Set aside.
Cream Butter & Sugar: Beat butter and sugar until fluffy (~3 minutes). Add eggs one at a time, then vanilla.
Combine: Alternate adding flour mixture and sour cream to the batter, beginning/ending with flour. Mix until just combined.
Filling: In a small bowl, mix brown sugar, cinnamon, and pecans.
Layer: Pour half the batter into the pan. Sprinkle filling evenly, then top with remaining batter.
Bake: 55–65 minutes, or until a toothpick comes out clean. Cool in pan for 15 minutes, then invert onto a rack.