Preheat oven to 325°F.
Lightly grease an 8 1/2 x 4 1/2 inch loaf pan, preferrably glass, and dust with flour.
In a bowl, whisk together flour, baking soda, and salt until well blended.
In a bowl for an electric mixer, beat together the butter, sugar, vanilla, and scraped vanilla beans from the split vanilla bean on medium to medium high speed until light and fluffy.
Add the eggs 1 at a time beating well after each addition until just blended.
Sprinkle half of the flour mixture over the egg mixture and stir until both are just incorporated. Stir in the sour cream, then sprinkle with the remaining flour mixture, and stir until evenly distributed.
Pour the batter into prepared loaf pan and tap gently on the counter to even out and settle the ingredients. Bake in a preheated oven until a toothpick inserted into the center comes out clean, about 70 minutes, or longer if using a metal pan.
Transfer the pan to a wire rack and let cool for 15 minutes. Run a thin knife around the inside of the pan, invert the cake on to the rack and lift off the pan. Place the cake on 1 of its sides and continue cooling. Serve warm or at room temperature.
If serving cake at room temperature (cool, not warm), sprinkle top of cake with confectioner's sugar if desired.