Preheat oven to 350 degrees.
In a medium mixing bowl, whisk together flour, salt, baking powder, and baking soda; set aside.
In the bowl of a stand-up mixer, beat butter on medium speed, until light and fluff, 4 minutes. Scrape down the sides of the bowl.
Gradually mix in sugar until blended. Continue to beat on medium, until fluffy, for another 3 additional minutes. Scrape down the sides of the bowl.
Add eggs, one at a time, mixing after each addition just until yolk disappears.
Mix in sour cream and vanilla extract. Scrape down the sides of the bowl.
Reduce mixer speed to low. Gradually add flour mixture and buttermilk alternately, beginning and ending with flour mixture, on low speed until just combined. Do Not overbeat! Scrape down the sides of the bowl with a rubber spatula, gently folding if needed, to make sure the batter is completely incorporated.
Generously butter a 12 cup bundt pan. Sprinkle 1/4 cup of sugar to the bottom of the greased pan and about 3 inches up the sides (mine always seems to go higher!), tapping the pan to ensure even distribution. Leave excess sugar in the pan. Sprinkle coconut flakes to the bottom of the pan.
Pour batter into pan and spread evenly. Tap pan on the counter to remove any air bubbles Bake in preheated oven until a skewer inserted into the center of the cake comes out with just a few moist crumbs, about 50-60 minutes.
Allow cake to cool in pan set on a wire rack, covered with a tea towel, for 15 minutes. Remove cake to a cake plate or stand and cool.