For the Cake

1. Preheat the oven to 325°F and set an oven rack in the middle position. Spray a 12-cup Bundt pan with nonstick cooking spray with flour, such as Baker's Joy or Pam with Flour.
2. In a medium bowl, whisk together the buttermilk, eggs, and vanilla. Set aside. (Note that the mixture will start to look curdled as it sits; that's okay.)
3. In the bowl of an electric mixer fitted with the paddle attachment or beaters, combine the flour, granulated sugar, baking powder, baking soda, and salt. Beat on low speed for 30 seconds to combine. Add the soft butter and half of the buttermilk mixture and mix on low speed until moistened but still a little crumbly, about 1 minute. With the mixer running on low, gradually add the remaining buttermilk mixture, then increase the speed to medium and mix for three minutes, stopping once to scrape down the sides and bottom of the bowl with a rubber spatula. The batter should look pale and creamy. Scrape down the sides and bottom of the bowl again, making sure the batter is evenly mixed.
4. Transfer the batter to the prepared pan and bake for 1 hour, or until a cake tester comes out clean. Set the pan on a cooling rack. Using a skewer or toothpick, poke about 40 holes in the bottom of the still-warm cake, going about ¾ of the way down. Spoon half of the glaze evenly over the bottom of the cake. If the glaze starts to pool on the surface, poke more holes to help it sink in. Leave the cake on the rack to cool for 30 minutes.
5. Invert the cake onto a serving platter. Brush or spoon the remaining glaze evenly over the top and sides of the cake, letting it soak in as you go. (Go slowly so that the glaze gets absorbed.) Let the cake sit for at least one hour before serving. Right before serving, use a fine sieve to dust the top of the cake with confectioners' sugar.

For the Glaze

1. In a small saucepan, combine the butter, granulated sugar, water, and vanilla. Bring to a boil, then reduce the heat and simmer until the sugar is dissolved, about 1 minute.
2. Note: If you’d like to make your own buttermilk, check out the easy method here.
3. Make-Ahead Instructions: This cake keeps well for several days. Once cool, store in a cake dome (or cover with plastic wrap) at room temperature until ready to serve.
4. Freezer-Friendly Instructions: The cake can be frozen for up to 3 months. After it is completely cooled, double-wrap it securely with aluminum foil or plastic freezer wrap, or place it in heavy-duty freezer bag. Thaw overnight on the countertop before serving.