Place a rack in the center of your oven. Preheat the oven to 325 degrees Fahrenheit 20 minutes before baking your bundt cake. Spray pan thoroughly with baking spray and set aside.
Combine flour, baking soda, and salt in a bowl and set aside.
Using a stand or electric mixer, cream butter on medium speed for one minute, or until smooth and creamy. Add granulated sugar, and continue to cream on medium speed for 4 minutes.
Add eggs one at a time, mixing on low only until incorporated. Slowly mix in vanilla extract. Be careful not to overmix after the eggs have been added to the batter.
With the mixer on low, alternately add the flour mixture and buttermilk in thirds. Begin and end with the flour mixture. Stir ingredients after each addition but only until just combined. Remove the bowl from the mixer and add black walnuts. Using a spatula, stir until just incorporated. Scrape down the sides of the mixer to ensure that all ingredients are well combined.
Spoon the batter into the prepared pan. Tap the pan on the counter a few times to remove any air bubbles. Bake for approximately 70 minutes. Halfway through the baking time, loosely cover the pan with aluminum foil to prevent over-browning. Once a toothpick inserted into the middle comes out clean, your pound cake is done.
Remove the cake from the oven and cool in the pan for only 10 minutes. Then loosen the cake around the edges if necessary. Invert the pan onto a cooling rack and lift the pan off gently. Once cool, dust with confectioners sugar.