To Make the Batter:

1. Preheat oven to 325°F.  It’s highly recommended to use an oven thermometer for this recipe, since proper oven temperature will impact the outcome of your cake.
2. Sift the all-purpose flour, baking soda, cream of tartar, and cinnamon together in a medium bowl. Set aside.
3. Place the granulated sugar in a large bowl or deli container. If using vanilla bean, add the vanilla beans to the sugar. Either massage the vanilla beans into the sugar, or put the top on the deli container and shake. Either way works, but the deli container is so satisfying.
4. Place the room temperature butter, cream cheese, and oil in a large mixing bowl, or the bowl of your stand mixer.  Mix on low speed until smooth.
5. Slowly add the granulated sugar/vanilla mixture and mix on medium speed until the mixture is light and fluffy.
6. Add eggs, one at a time, mixing until each one is fully incorporated.  Scrape the sides and bottom of the bowl as needed.  Don’t skimp on this step because it helps the cake rise! 
7. If using pure vanilla extract, add extract and mix until thoroughly combined.
8. Add half of the flour mixture and mix on lowest speed until nearly combined.
9. With the mixer on the lowest speed, add all of the buttermilk and mix until just combined. 
10. Add the second half of the flour mixture and mix on low speed until nearly combined.  Stop mixing just before the mixture is fully together.
11. Using a rubber spatula, fully scrape the sides and bottom of the mixing bowl.  Then, stir the batter until it is smooth and consistent.  Make sure to fully scrape the bottom of the bowl during this step!
12. Grease a 10-12 cup bundt pan as you normally would and place the batter in the pan.
13. Bake the cake at a true 325°F for 60-70 minutes, or until an instant read thermometer reads 210°F-215°F.  My preferred internal temperature for this cake is 212°F.  Alternately, the cake is done with a toothpick inserted into the center comes out clean and a fingerprint indentation bounces back.
14. Allow the cake to rest for ten minutes while you make the simple syrup.

To Make the Cinnamon Simple Syrup:

1. Combine sugar, water, salt, and cinnamon in a small saucepan and bring to a boil.  Stir occasionally until the sugar is completely dissolved.
2. Remove the simple syrup from the heat and add vanilla. Stir until incorporated.
3. Allow the cake to cool completely, then use a pastry brush, gently brush the cinnamon simple syrup over the entire cake.

To Make the Snickerdoodle Glaze:

1. Combine the confectioner’s sugar, vanilla, cinnamon, salt, and 2 tablespoons of the whole milk in a medium bowl.  (see note about glaze, below.)
2. Stir with a spoon until nearly combined, adding additional milk 1/2 teaspoon at a time if necessary.  Stir until smooth.  The glaze will be the consistency of thick honey.
3. Using a spouted measuring cup, spoon, or squeeze bottle, drizzle final glaze over the cake.  For this cake, I used a spouted measuring cup.
4. If necessary, use a spoon to help the glaze fall over the sides of the cake.
5. Allow the glaze to set for five minutes, then gently sprinkle decorating sugar (if using) to finish.

To Store:

This cake can remain on a countertop overnight, or it can be stored in a refrigerator for up to a week.