To Make the Cinnamon Streusel Filling:

1. Add the brown sugar, granulated sugar, flour, and salt to a medium bowl.  Stir to combine.
2. Cut the cold butter into tablespoon-sized pieces and add to the sugar mixture.  Use fingers or a pastry cutter, break up the butter pieces until they are the size of peas or larger.
3. Refrigerate until ready to use.

To Make the Cake:

1. Set your oven to a true 325°F.  An oven thermometer is extremely useful here, since most home ovens will not reach 325°F when set to 325°F.
2. Place the granulated sugar and brown sugar in a bowl and set aside.
3. Sift together the all-purpose flour, kosher salt, cinnamon, and baking soda in a medium bowl.  Set aside.
4. Add the room-temperature butter to the bowl of your stand mixer or a large mixing bowl.  Mix with your hand mixer or stand mixer until the butter is completely smooth. Once the butter is smooth and combined, add the sugar mixture and cream until the mixture is light and fluffy.
5. Add the eggs, one at a time, mixing each egg until completely incorporated into the mixture.  Scrape the sides and bowl as needed to ensure even mixing.
6. Add the vanilla extract and mix thoroughly.
7. Add half of the flour mixture and mix until just combined.
8. Add all of the sour cream and mix until just combined.
9. Add the second half of the flour mixture and mix until just combined.  Using a rubber spatula, give the sides and bottom of the bowl a final scrape to ensure that the batter is evenly mixed.
10. Prep a 12- or 15-cup bundt pan as you normally would (I use butter and flour to prep pans for this cake).  Add half of the batter, then top with as much of the streusel mixture as you’d like (I use all of it, even though it seems like a lot!).  Add the second half of the batter atop the streusel mixture.
11. Tap the bundt pan several times on the counter to move the batter to the edges and remove any large bubbles from the batter.
12. Bake for 65-75 minutes in a true 325°F oven, or until an instant-read thermometer reads 212°F-215°F.  Allow to cool on a wire rack for ten minutes, then invert the cake and remove from the pan.

To Make the Vanilla Simple Syrup:

1. Add the water, granulated sugar, and fine sea salt to a small saucepan.  Bring to a boil and boil just until all of the solids are dissolved.  Remove from the heat.
2. Add the vanilla extract and stir to combine.
3. Brush on the cake after inverting it onto the cooling rack.  Allow the cake to cool completely.

To Make the Vanilla Glaze:

1. Add the confectioner’s sugar, fine sea salt, vanilla extract, and three tablespoons of whole milk to a medium mixing bowl.  Stir until the confectioner’s sugar is moistened, or until you notice that the milk is no longer moistening the confectioner’s sugar. 
2. Add additional milk, 1/2 tsp-1 tsp at a time, stirring until each addition is fully incorporated.  Be deliberately slow about adding additional liquid, because it takes a deceivingly-small amount of liquid to make an excellent glaze.
3. Continue stirring the mixture until it is completely smooth.  If needed, add milk, a half teaspoon at a time, until it is the texture of thick honey.
4. The final glaze should have the consistency of thick honey.
5. Pour over the completely cooled cake with a spouted measuring cup, squeeze bottle, or spoon.
6. Enjoy!