Step 1

Place 3 sticks of the unsalted butter in a stand mixer (or large bowl if using an electric hand mixer). Place 5 large eggs and 1 cup buttermilk on the counter. Let everything sit at room temperature until the butter is softened, at least 1 hour.

Step 2

Arrange a rack in the middle of the oven and heat the oven to 325ºF. Meanwhile, place the remaining 1 tablespoon unsalted butter in a small microwave-safe bowl and microwave until melted, 20 to 30 seconds. Add 1 tablespoon of the all-purpose flour and mix to form a smooth paste. Brush the paste on the inside of a 12-cup bundt cake pan (see Recipe Notes), making sure to thoroughly coat the tube and all the crevices.

Step 3

Place the remaining 2 3/4 cups all-purpose flour and 1 1/4 teaspoons kosher salt in a medium bowl and whisk to combine. Add vanilla of choice to the buttermilk and whisk until combined.

Step 4

Beat the butter on medium speed with the paddle attachment until lightened in color and fluffy, 3 to 4 minutes. With the mixer on still on medium speed, gradually add 2 cups granulated sugar and beat until fluffy, about 3 minutes. Stop the mixer and scrape down the paddle and sides of the bowl. Beat in the eggs one at a time, making sure each egg is fully incorporated before adding the next, about 1 1/2 minutes total. Stop and scrape down the bowl again.

Step 5

With the mixer on the lowest speed, beat in 1/3 of the flour mixture, then 1/2 of the buttermilk mixture. Beat in 1/2 of the remaining flour mixture, then all of the remaining buttermilk mixture. Beat in the remaining flour mixture until just combined. Scrape the batter into the bundt pan and smooth out the top. Pick up the pan and gently tap on the work surface a few times to remove any air bubbles.

Step 6

Bake until light golden brown and a tester inserted into the center of the cake comes out clean, 1 hour and 10 minutes to 1 hour and 25 minutes. Place the bundt pan on a wire rack and let cool 30 minutes (the cake will pull away from the sides of the pan). Flip the cake out onto the rack and let cool completely, about 1 1/2 hours more. Sift powdered sugar over the top if desired before slicing and serving.