Preheat the oven to 325°. Spray a bundt pan very well with baking spray, then coat with flour. Turn the pan upside down to let any excess flour fall out. In a large mixing bowl combine flour, salt, baking powder and baking soda. Set aside.
In the bowl of a stand mixer fitted with a paddle attachment combine sugar and butter. Beat together on medium-high for 1 minute. Stop the mixer and scrape down the sides of the bowl with a rubber spatula. Add in the eggs and mix for 30 seconds. Add in buttermilk, sour cream and vanilla and mix to combine. Add in the flour mixture and mix until just incorporated.
Transfer the batter into the prepared bundt pan, then place into the preheat oven on the center rack. Bake for 1 hour, until a toothpick inserted into the cake comes out clean or with a few moist crumbs. Once baked, remove from the oven and place onto a wire cooling rack.
Butter Sauce Directions:
Add sugar, butter, water and vanilla to a small saucepan and mix to combine. Cook over medium heat, until the mixture reaches a simmer. Simmer for 1 minute, until the sugar has dissolved. Remove from heat.
Assembly:
Let the cake cool for 10 minutes, then poke holes into the cake using the handle of a wooden spoon or chopstick. Pour the butter sauce onto the cake and let soak. Once the butter sauce has been absorbed, flip the cake onto a cake stand to release and let cool completely. Make sure to do this while the cake is still warm to help with a clean release. Once the cake has cooled, dust with powdered sugar.
Notes
Storage: Cake may be stored in an airtight container for up to 3 days.