To Make the Red Velvet Marble Cake:

1. Take out your digital kitchen scale and a bunch of bowls/containers.  This is a messy endeavor but the results are worth it.  A digital kitchen scale will yield the absolute best result.
2. Use your digital kitchen scale to measure the weight of your main (first) mixing bowl (use grams!).  Write down the weight and keep it handy.
3. Before you begin, tare (or “zero”) the weight of both of the mixing bowls that you’ll be using for the cake batters.  One should be the mixing bowl where you start the batter (the main bowl), and the second one will be used once you separate the single batter into two batters.  Not sure how to tare the weight of your bowls?  Start here!
4. Sift together 192 g (1.5 c) of the all-purpose flour, 1/2 tsp of kosher salt, and 1/4 tsp of baking soda in a medium bowl. Set aside.
5. Sift together 160 g (1.25 c) of all-purpose flour, cocoa powder, 1/4 tsp baking soda, and 1/2 tsp kosher salt in another medium bowl.  Set aside.
6. Combine whole milk and white vinegar in a measuring cup or deli cup.  Divide into two equal parts and set both aside.
7. In the first (main) mixing bowl, cream butter and oil until very smooth.  Add sugar to the butter/oil mixture and cream until light and fluffy.  Scrape bowl frequently to encourage even mixing.
8. Add eggs, one at a time, mixing until there is no evidence of the prior egg before adding the next egg.  Scrape the bowl as needed to encourage even mixing.
9. Add vanilla extract and mix thoroughly. 
10. Weigh the batter in the main bowl by placing the main bowl on your digital kitchen scale.  Subtract the bowl weight from the new weight.  This is your batter weight. 
11. Remove half of the batter from the main bowl and place it into the second bowl.  In the main bowl, add half of the sifted flour mixture and mix on low speed until it is nearly combined.  Add half of the “buttermilk” and once again mix on low speed until nearly combined.  Then add the second half of the flour mixture and mix on low speed until nearly combined.  Use a stiff spatula to scrape the sides of the mixing bowl and fold the batter together for a cohesive vanilla cake mixture.  Set aside while you work on the second bowl.
12. To the second bowl, add half of the sifted flour/cocoa mixture and mix on low speed until it is nearly combined.  Add half of the “buttermilk” and the red food coloring and once again mix on low speed until nearly combined.  Then add the second half of the flour/cocoa powder mixture and mix on low speed until nearly combined.  Use a stiff spatula to scrape the sides of the mixing bowl and fold the batter together for a cohesive red velvet cake mixture.  Set aside while you prep your bundt-pan.
13. Prep a 10-12 cup bundt pan as you normally would.
14. Using two different standard-sized ice cream scoops, layer the vanilla and red velvet cakes, alternating between each flavor.  There is no need to “marble” with a knife; the baking process will do that for you.  If you want more swirls, it is fine to use a knife to encourage more marbling.
15. Bake for 65-75 minutes or until 212°F internal temperature.  While baking, make the simple syrup.

To Make the Vanilla Simple Syrup:

1. Add the granulated sugar, water, and fine sea salt to a small saucepan.  Bring to a boil and allow to boil only until the solids are dissolved.
2. Remove  from the heat and add pure vanilla extract.  Stir to combine.
3. Allow to cool completely, then add to the completely cooled cake with a pastry brush. 

To Make the Cream Cheese Glaze:

1. Add the room-temperature cream cheese to a large mixing bowl or the bowl of a stand mixer.  Mix on lowest speed until completely smooth.
2. Add the confectioner’s sugar, 1.5 tbsp of the whole milk, and vanilla extract to the bowl.  Mix with a small whisk until there are no more lumps.  A power mixer is not advised at this point if you want a smooth cream cheese glaze with no air bubbles.  (And no air bubbles is the goal!)
3. Use a spouted measuring cup, spoon, or squeeze bottle to add the glaze to the completely cooled cake.  If the cake is too warm, the glaze will just heat up and much of it will simply fall off of the cake.
4. Enjoy!