Preheat the oven to 350°F (175°C) and line a 9 by 5 inch loaf pan with parchment paper, leaving an overhang for easy removal.

In a medium bowl, whisk together the all-purpose flour, baking powder, and salt until combined and no lumps remain.

In another bowl, beat the softened butter and granulated sugar with a whisk or hand mixer for 2 to 3 minutes until pale and fluffy.

Add the eggs one at a time to the butter mixture, whisking well after each addition to fully incorporate.

Stir in the vanilla extract, then alternate adding the dry ingredients with the sour cream and milk, beginning and ending with the dry ingredients, mixing just until incorporated.

In a small bowl, combine chopped pecans, brown sugar, granulated sugar, melted butter, flour, vanilla extract, and salt; stir until mixture resembles damp sand.

Pour half of the batter into the prepared pan and smooth the top, then sprinkle half of the pecan streusel evenly over the batter.

Add the remaining batter and spread evenly, then top with the remaining streusel, pressing gently so it adheres to the batter.

Bake for 50 to 55 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs and the top is golden brown; if browning too quickly, tent with foil.

Let the bread cool in the pan for 15 to 20 minutes, then lift it out using the parchment overhang and transfer to a cooling rack to cool completely before slicing.