Preheat oven to 350 degrees F.
Grease a glass 9x13 inch baking dish. Set aside.
In a mixing bowl, beat together butter and cream cheese until creamy, about 2 to 3 minutes.
Add in brown sugar and white sugar. Beat until fluffy, about 2 to 3 minutes.
Beat in both eggs until combined.
Beat in vanilla extract until combined.
In a separate bowl stir together flour, baking soda, baking powder, cornstarch, and salt.
Slowly beat in a third of the dry mixture into the wet then add in half the buttermilk. Then beat in another third of the dry mixture and the rest of the buttermilk. Then beat in the remaining dry mix into the wet. Beat just until combined, do not over mix.
Pour half the batter into the prepared baking dish. The batter will be thick.
Stir together sugar and cinnamon. Sprinkle evenly over the first layer of batter in the baking dish. Then carefully top evenly with the rest of the cake batter.
Whisk together flour, brown sugar, sugar, and cinnamon until well combined. Stir in melted butter with a fork until it is a crumbly mixture and there is no more visible white flour. Sprinkle over top of cake.
Bake cake for 45 to 50 minutes or until a toothpick inserted in the middle comes out clean. Let the cake cool before adding glaze.
Stir together powdered sugar and milk. Drizzle over top of completely cooled cake.