Preheat the oven to 325°F and grease and flour a 12-cup (10-inch) Bundt tin.
Mix the flour with the baking soda, baking powder, and salt in a bowl.
Mix the buttermilk with the vanilla in another bowl.
Beat the sugar with the butter using a stand mixer on medium-high for several minutes, or until fluffy and light, scraping down the sides as you go.
Turn the speed down a little and add the eggs, one at a time, beating until well blended.
Now turn the speed down as low as you can, adding the flour mixture to the buttermilk mixture, incorporating the butter mixture as well.
Spoon the finished batter into the prepared Bundt tin.
Tap the Bundt tin on the countertop a couple times to get rid of any air bubbles.
Bake for about 55 minutes or until a toothpick inserted into the center comes out clean.
Let the cake cool on a wire rack (still in the Bundt tin) for 30 minutes.
Meanwhile, heat the water, sugar, butter, and salt in a pan over a low heat, to make the glaze, stirring frequently.
Don’t let it boil.
Whisk in the cinnamon and vanilla.
Run a knife around the edges of the cake to get it out of the tin.
Poke holes in the cake with a chopstick, skewer or large fork, going about ¾ of the way into it.
Put ¼ cup of the glaze to one side and spoon the rest over the cake bottom.
Once the glaze has set, flip the cake over, so the top is facing up.
Warm the glaze back up and brush it over the top, sides and inside of the cake.
Let it sit for another hour before serving.
Slice and serve.