To Make the Cake:

1. Get the tare weight of your primary mixing bowl, using your digital kitchen scale. (Don’t know what “tare weight” means? Check out this post!)
2. Set oven to a true 325°. An oven thermometer will help you determine whether your oven is actually the correct temperature. 
3. Sift together 117 grams of all-purpose flour, ½ teaspoon of baking soda, 44 grams of natural cocoa powder, and ½ teaspoon kosher salt into a medium bowl. Set aside. 
4. Sift together 192 grams all-purpose flour, ¼ teaspoon baking soda, and ½ teaspoon kosher salt in a second bowl. Set aside.
5. Split 250 grams of buttermilk into two small containers. Add ½ tablespoon oil to each liquid container and combine.
6. This step is very important! For this recipe, you’ll need two mixing bowls. Your primary mixing bowl, where you’ll make your chocolate cake batter, and your secondary mixing bowl, where you’ll make your vanilla cake batter. Before you start (in your primary bowl), you need the bowl weight of each bowl. Write down the bowl weight for each bowl and set that aside where you’ll be able to find it quickly later.
7. Place all of the butter into your primary mixing bowl. Mix on medium speed until the butter is completely smooth.
8. Add the granulated sugar and cream the mixture until light and fluffy. (psst…don’t know what it means to “cream until light and fluffy”? Take a look at this article!) Scrape the sides and bottom of the bowl as necessary to ensure even mixing.
9. Add eggs, one at a time. Mix each egg until it’s fully incorporated before adding the next egg. Scrape the sides and bottom of the bowl as necessary to ensure even mixing. The batter might look curdled and that is okay.
10. Add all of the pure vanilla extract and mix until fully combined.
11. *Critical Step* Place 1/2 of the batter into a second mixing bowl. To do this, follow these steps: a) Weigh the primary mixing bowl while it is full with all of the batter; subtract the weight of the empty mixing bowl, using your note from earlier (this is your batter weight); and c) divide the remaining weight by 2 to figure out how much batter needs to be added to the second bowl. Then, remove that amount of batter from the primary mixing bowl into the second mixing bowl. 
12. To finish the chocolate batter: Add half of the flour/cocoa mixture and mix on low speed until nearly combined. Scrape the sides and bottom of the bowl as necessary.
13. Add the first buttermilk/oil mixture to the chocolate batter, and mix on low speed until nearly combined.
14. Add the second half of the flour/cocoa mixture and mix on low speed until nearly combined. Scrape the sides and bottom of the bowl with a stiff spatula, and fold the batter until it is smooth and combined. Set the chocolate cake batter aside while you prepare the vanilla cake batter.
15. To finish the vanilla batter: Add half of the flour mixture and mix on low speed until nearly combined. Scrape the sides and bottom of the bowl as necessary.
16. Add the buttermilk/oil mixture and mix and mix on low speed until nearly combined.
17. Add the second half of the flour mixture and mix on low speed until nearly combined. Scrape the sides and bottom of the bowl with a stiff spatula, and fold the batter until it is smooth and combined. 
18. Prepare a 10- or 12-cup bundt pan as you normally would. Use an ice cream scoop to place a layer of chocolate batter around half of the pan; fill in the second half with vanilla. Continue to layer in this way (chocolate scoops around half the pan, then vanilla scoops to finish the layer). To settle the batter into the pan, give it several taps on the counter with a straight up and down motion. Do not shake the pan, as it will cause the batters to swirl together more. 
19. Bake at 325° for 60-70 minutes, or until the internal temperature of the cake reaches 212°F.
20. Remove the pan from the oven. After ten minutes, remove the cake from the pan by inverting the pan onto a cooling rack. Allow to cool completely.

To Make the Vanilla Simple Syrup:

1. Place granulated sugar, water, and salt in a small saucepan. Bring to a boil.
2. Remove from the heat and add pure vanilla extract. Stir to combine.
3. Allow the simple syrup and the cake to cool completely, then brush the simple syrup on to the completely cooled cake.

To Make the Rich Vanilla Glaze:

1. The name of the game for a smooth glaze is to stir gently. This glaze has heavy cream, and if it’s agitated too much during the mixing process, it will develop bubbles and attempt to transform to whipped cream. To avoid this, stir very gently. Practice is key here too!
2. Place the confectioner’s sugar, fine sea salt, pure vanilla extract, ½ tablespoon of whole milk, and ½ tablespoon of heavy cream in a medium mixing bowl. 
3. With a small whisk, very gently stir, until the confectioner’s sugar is fully hydrated by the liquid. It will seem like there is too much confectioner’s sugar, but if you continue stirring, it will eventually get moistened by the initial liquid amounts. (It will likely be in a ball in your whisk, and that’s to be expected.)
4. Add ½ teaspoon of heavy cream, and another ½ teaspoon of whole milk. Continue stirring very gently, until the glaze is the consistency of very thick honey. 
5. Use a spouted measuring cup or spoon to pour the glaze over the center of the cake. Gravity will take the glaze over the sides. This glaze recipe makes a very conservative amount of glaze; that was intended, since I didn’t want to completely cover the beautiful cake design with glaze.
6. Enjoy!