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. Combine flax meal and water thoroughly in a small measuring cup or bowl.  Set aside.
3. Combine the plant-based milk and lemon juice in another small measuring cup.  Set aside to “sour”.
4. Sift the flour, baking soda, and salt in a medium bowl.
5. Carefully cut open the vanilla bean pod.  Scrape the seeds from the pod and add them to the sugar in a small bowl or deli cup. Either massage the vanilla beans with your fingertips in the bowl, or shake the vanilla beans in the sealed deli cup.
6. Place the remaining vanilla bean pod in the plant-based buttermilk until ready to use.
7. Place the room-temperature plant-based butter and vegetable oil in a large mixing bowl or the bowl of a stand mixer.  Mix on medium speed until smooth.
8. Add the vanilla/sugar mixture and mix until light and fluffy. Scrape the sides and bottom of the bowl as necessary to ensure even mixing.
9. Add half of the flax eggs and mix until it is fully incorporated.  Add the second half of the flax egg mixture and mix until fully combined. Scrape the sides and bottom of the bowl as necessary to ensure even mixing.
10. Add vanilla extract (if using) and mix until thoroughly combined.  If using vanilla bean, skip this step.
11. Add half of the flour mixture and mix on low speed until combined.
12. Remove the vanilla bean from the plant-based buttermilk.  Add all of the plant-based buttermilk and mix on lowest speed until just combined.
13. Add the second half of the flour mixture and mix on low speed until almost combined.  Stop mixing just before the mixture is fully together.  
14. Using a rubber spatula, fully scrape the sides and bottom of the mixing bowl.  Then, mix the batter until it is smooth and consistent.  Make sure to fully scrape the sides and bottom of the bowl!
15. Grease a 10-12 cup bundt pan with the remaining butter and flour and place the batter in the pan.
16. 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.
17. Allow the cake to rest for ten minutes, the invert onto a cooling rack and remove the cake pan. Allow the cake to cool completely.

To Make the Lemon Simple Syrup:

1. Combine sugar, water, and salt 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 lemon juice and vanilla. Stir until incorporated. Allow to cool completely.
3. Using a pastry brush, gently brush the cooled lemon simple syrup over the entire cake.

To Make the Lemon Glaze:

1. Combine the confectioner’s sugar, vanilla, fine sea salt, and 2 tablespoons of lemon juice in a medium bowl.
2. Whisk until nearly combined, then add up to 1 more tablespoon of lemon juice if necessary, 1/2 teaspoon at a time.  Whisk until smooth.  The glaze will be thick but should be pourable.
3. The final glaze should have the consistency of thick honey, and you should just be able to pour it. 
4. Using a spouted measuring cup, spoon, or squeeze bottle, drizzle final glaze over the cake.
5. If necessary, use a spoon to help the glaze fall over the sides of the cake.
6. Allow the glaze to set for five minutes, then gently sprinkle decorating sugar (if using) to finish.