Preheat the oven to 325°F. Butter and flour a 10- to 12-cup Bundt pan.
In a large bowl, whisk together flour, salt, baking powder, and baking soda.
In a large mixing bowl or a stand mixer fitted with a paddle attachment, beat the butter and sugar at medium speed until fluffy, 3 to 4 minutes, stopping to scrape sides of bowl occasionally. With the mixer on low, add the eggs, one at a time, beating well after each addition.
With the mixer on low, gradually add the flour mixture to the butter mixture alternately with the milk, beginning and ending with flour mixture, beating just until combined after each addition. Spoon the batter into the prepared pan.
Bake for 1 hour or until a wooden pick inserted near the center comes out clean.
Right when the cake is out of the oven, combine the butter, sugar, and water in a small saucepan. Bring to a simmer over medium heat, stirring constantly. Cook, stirring constantly, until opaque and slightly thickened, about 2 minutes. Remove from heat, and stir in the vanilla.
Pour over the cake in the pan. Let cool for 15 minutes. Invert the cake onto a wire rack, and let cool completely before serving. Store the cooled cake covered at room temperature for up to 5 days.
