Preheat your oven to 350°F (175°C). Generously grease your bundt pan with butter or non-stick spray and dust it lightly with flour, tapping out any excess.
In a large bowl, whisk together the granulated sugar and melted butter until smooth. Add the eggs, one at a time, beating well after each addition. Stir in the buttermilk and scrape the seeds from the vanilla bean pod (or add the vanilla extract) into the mixture. Mix until combined.
In a separate bowl, sift together the cake flour, baking powder, and salt.
Gradually add the dry ingredients into the wet ingredients, mixing gently just until combined. Be careful not to overmix; a few lumps are okay.
Pour the batter evenly into your prepared bundt pan, smoothing the top with a spatula. Bake for 40-45 minutes, or until a toothpick inserted into the center comes out clean.
Let the cake cool in the pan on a wire rack for about 15-20 minutes. Then, carefully invert the pan to release the cake onto the rack and allow it to cool completely before glazing.