The oven has to be preheated to 325 degrees F. Prepare a 10-inch (12-cup) Bundt pan by greasing and flouring it liberally.
Flour, baking powder, baking soda, and salt should be mixed in a medium bowl. Leaving aside. Combine vanilla extract with buttermilk and leave aside.
Put the sugar and butter in the bowl of a stand mixer fitted with the paddle attachment, and beat on medium-high speed for at least three or four minutes (no less! ), until the mixture is light and fluffy. Turn the mixer speed down to medium and add the eggs one by one, mixing after each addition just until the yolks are completely incorporated.
Put the mixer on low and add the flour mixture to the butter in thirds, alternating with the buttermilk. Beat until barely mixed, then give the batter a last stir by hand to incorporate any flour that may have settled to the bottom.
Once the Bundt pan has been prepped, transfer the batter to it and tap it on the counter a few times to get rid of any air bubbles. Cook for 50-60 minutes at 325 degrees F, or until a wooden pick inserted into the center of the cake comes out with a few crumbs.
After 5 minutes, set the cake on a cooling rack, and using the thin end of a chopstick, make holes all over the cake, going approximately 3/4 of the way down. To make the holes bigger, you can use the back of a spoon or a skewer instead.
Make the Butter Glaze just after you poke holes in the cake. Put the sugar, butter, water, and salt in a medium pot and stir to combine. Melt on low heat, stirring regularly, making sure the mixture doesn't boil. When the butter has melted, add the vanilla and cinnamon (if using).
Put aside a quarter cup of the glaze for later use. Carefully drizzle the remaining Glaze over the top (now bottom) of the cake, taking your time so that it may seep into the holes and not spill over the sides.
After 30 minutes (no longer or the glaze will set like glue), loosen the sides of the cake with a knife and invert it onto a plate or cake stand.
Reheat the Glaze (but don't let it boil) and carefully brush it all over the cake after it's cooled entirely. The cake is best served after resting for at least an hour, but overnight is best for optimal texture and flavor. If you're not going to serve the cake right away, cover it securely in plastic wrap and leave it at room temperature.
It's great with just whipped cream or fresh fruit, but it's even better with fresh berries and strawberry or raspberry sauce!