Gather all ingredients.
Preheat the oven to 325 degrees F (165 degrees C). Grease and flour a 10-inch Bundt pan.
Make the cake: Mix flour, sugar, salt, baking powder, and baking soda together in a large bowl. Blend in buttermilk, butter, eggs, and vanilla with an electric mixer. Beat for 3 minutes on medium speed. Pour batter into the prepared pan.
Bake in the preheated oven until a wooden toothpick inserted into the center of the cake comes out clean, about 1 hour.
When the cake is almost finished baking, make the butter sauce: Combine sugar, butter, water, and vanilla in a saucepan over medium heat. Cook and stir until fully melted and combined; do not boil.
Remove the cake from the oven. Prick holes in the still-warm cake, then slowly pour butter sauce over the top.
Let cake cool before removing from pan, about 30 minutes.
