Preheat oven to 325 degrees F. Generously grease and flour a 10" tube or Bundt pan (or brush the inside of the pan generously with cake goop).
In a medium pitcher/measuring cup, whisk together the eggs, dulce de leche, sour cream and vanilla extract. Set aside.
6 eggs, 1 cup dulce de leche, 1/2 cup sour cream, 2 teaspoon vanilla extract
Place the vanilla bean and both sugars in the bowl of a food processor fitted with the metal blade and pulse until the vanilla bean is finely ground. Sift the sugar and vanilla bean through a fine-mesh sieve into the bowl of a stand mixer.
1 cup toasted sugar, 1/2 cup brown sugar, 1 vanilla bean
Sift the flour, cake flour, baking powder and salt into the mixing bowl and stir to combine.
2 cup all purpose flour, 2/3 cup cake flour, 1 1/2 teaspoon baking powder, 1 teaspoon salt
Cut the butter into chunks and add to the mixing bowl. Using a paddle attachment, mix on low speed until the mixture resembles coarse crumbs or wet sand.
2 cup unsalted butter
With the mixer running, slowly add about half of the liquid mixture. Scrape down the sides and bottom of the bowl. Increase the speed to medium and beat for about 1 minute to combine well and build some structure.
Reduce the speed back to low and gradually add the remainder of the liquid. Increase speed to medium and beat for another minute.
Pour the batter into the prepared pan and smooth the top. Bake until the top is dark golden brown and a tester comes out with a few moist crumbs (this may take 60-75 minutes) Cool in the pan for about 10-15 minutes before unmolding onto a wire rack.
To make the glaze (optional)
In a small mixing bowl, combine the cream cheese, milk, vanilla and salt. Beat until creamy. Add the powdered sugar and whisk until smooth. The glaze should fall of your whisk in ribbons. If it is too thick, add more milk. If it is too thin, add more powdered sugar.
Place a sheet of wax paper under the wire rack the cake is on to catch any drips. Slowly pour the glaze over the top of the cake allowing it to run naturally down the sides of the cake. Let the glaze set slightly, then drizzle the dulce de leche in thin lines over the surface of the glaze (radiating out from the center and down the sides). You can heat the dulce de leche in 5-10 second burst in the microwave to loosen it and make it easier to drizzle.
2 tbsp dulce de leche
Notes
If you are not using the vanilla bean, simply add the sugar to the bowl of your stand mixer along with the other dry ingredients and butter.
If your pan is not quite big enough, fill it to only 2/3 full and use any leftover batter to bake a small loaf or some cupcakes.