Preheat oven to 325°F (165°C). Grease and flour a Bundt pan.
In a large bowl, whisk together the flour, sugar, salt, baking powder, and baking soda.
Add the butter, buttermilk, vanilla, and eggs. Beat until smooth and well combined.
Pour the batter into the prepared Bundt pan and spread evenly.
Bake for 60 minutes, or until a toothpick inserted into the center comes out clean.
While the cake is baking, make the butter sauce. In a saucepan, combine the sugar, butter, and water. Cook over medium heat until the butter is melted and the sugar is dissolved. Remove from heat and stir in the vanilla extract.
When the cake is done, remove it from the oven and poke holes all over the cake with a skewer or fork. Pour the butter sauce over the hot cake, allowing it to soak in.
Let the cake cool in the pan for 30 minutes, then invert onto a serving plate. Serve warm or at room temperature.