Preheat the oven to 350°F (175°C) and grease a 10-inch Bundt pan with butter or cooking spray and dust lightly with flour.

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

In a large bowl, cream the softened butter and granulated sugar using an electric mixer until light and fluffy, about 3-5 minutes.

Add the eggs one by one, mixing well after each addition, then add the vanilla extract.

Alternately mix in the flour mixture with the sour cream and whole milk, beginning and ending with the flour mixture.

In a small bowl, mix together the brown sugar, ground cinnamon, and chopped pecans (if using).

Pour half of the batter into the prepared pan, sprinkle the cinnamon sugar mixture, and top with the remaining batter.

Use a knife to swirl through the batter gently to create a marbled effect.

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

Cool in the pan for 15 minutes before inverting onto a wire rack to cool completely for 45 minutes.

In a small bowl, whisk together powdered sugar, milk, and vanilla extract until smooth.

Drizzle the glaze over the cooled cake before serving.