Preheat your oven to 350°F (175°C) and grease and line a 9x5-inch loaf pan with parchment paper.

In a medium bowl, whisk together the flour, baking powder, baking soda, and salt and set aside.

In a large bowl, cream the softened butter and granulated sugar until light and fluffy, about 2-3 minutes.

Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.

Mix the sour cream and whole milk into the batter until smooth.

Gradually fold the dry ingredients into the wet batter until just combined.

In a small bowl, mix the chopped pecans, brown sugar, and ground cinnamon.

Pour half the batter into the prepared loaf pan, add half the pecan filling, then the remaining batter, and top with the rest of the pecan filling.

Swirl gently with a knife to create a marbled effect.

Bake for 50-60 minutes or until a toothpick inserted into the center comes out clean.

Let the cake cool in the pan for 10 minutes before transferring to a wire rack.

Whisk together powdered sugar, 2-3 tablespoons milk, and a splash of vanilla until smooth and drizzle over the cooled loaf.