Preheat oven to 325 degrees. Coat a bundt pan generously with nonstick cooking spray.

Combine flour, salt, baking powder and baking soda together in a large bowl.

In the bowl of a stand mixer, beat the cup of butter and sugar on medium speed until fluffy. (Alternatively, use a handheld electric mixer and a large bowl). Add the eggs, vanilla and buttermilk. Beat to combine. With the mixer on low speed, add the dry mixture until incorporated.

Pour batter into the prepared bundt pan. Bake for in the preheated oven for 60 minutes, until a toothpick inserted into the cake comes out clean.

Make the butter sauce: in a small saucepan combine the butter, sugar, milk and vanilla. Heat the mixture over medium-low heat until the sugar dissolves and the mixture becomes smooth.

Prick holes in the warm cake and pour the butter sauce over the cake. Do not worry if there's a lot of sauce - it will all sink in.

Cool the cake completely in the bundt pan. Invert the room temperature cake onto a serving plate. Top with caramel sauce and flaky sea salt.