Preheat oven to 350° & lightly grease a 6 cup nonstick bundt pan.

In a medium bowl, whisk together flour, baking powder, baking soda, cinnamon & 1/4 tsp. salt.

In a large bowl, whisk together brown sugar, 1/4 cup sour cream, oil, egg & vanilla until smooth. Stir in carrots, pineapple & walnuts.

Stir in flour mixture until just combined. Pour batter into prepared pan & bake until toothpick comes out clean (about 55 minutes).

Using a wooden spoon, beat confectioner's sugar & butter until smooth. Whisk in remaining 1/4 cup sour cream & 1 pinch salt.

Drizzle over top of cake & sprinkle with cinnamon.