Directions

1. Coat 12-cup Bundt pan with nonstick spray. Sift salt, baking soda, and cake flour into a medium bowl then combine with a spoon.
   
2. In a stand mix with a whisk attachment add 1 1/2 cups butter then whip on high speed, about 1 minute. With motor running gradually stream in sugar and beat until mixture is pale and fluffy, about 5 minutes.
   
3. Add eggs one at a time, beating well after each addition and scraping down sides of bowl with a spatula. Reduce speed to low and with motor running, gradually add flour mixture in 2 additions, beating until just incorporated after each addition.
   
4. Beat in sour cream, oil and 1 tablespoon vanilla, scraping down sides of bowl as needed, until combined.
   
5. Place a rack in upper third of oven; preheat to 350 degrees. In a small bowl whisk brown sugar, 5 tablespoons melted butter, flour, cinnamon and 1 teaspoon vanilla. Scrape 1/3 of batter into prepared pan. Drizzle half of the cinnamon mixture over. Using a butter knife, swirl cinnamon mixture through batter. Top with half of remaining batter; drizzle remaining cinnamon mixture over and swirl together again. Scrape remaining cake batter into pan and smooth surface.
   
6. Bake cake until a tester inserted in the center comes out with only a few moist crumbs attached, 80-90 minutes. Transfer pan to a wire rack and let cake cool for 10 minutes. Turn out cake onto rack, let cool completely.
   
7. Meanwhile, add cream cheese and 2 tablespoons butter (room temperature) to standing mixer with a whisk attachment. Beat medium-high speed until combined, about 2 minutes. Reduce speed to medium and gradually add powdered sugar in two batches, scraping down sides of bowl. Continue to beat until incorporated, then increase speed to medium-high and stream in milk and vanilla. Beat until icing is smooth and pourable, about 2 minutes.
   
8. Drizzle cooled cake with icing over the top, letting it drip down the sides. Transfer to the refrigerator and chill until icing is set, about 15 minutes. Transfer cake to a large plate to serve.