Preheat oven to 350°F. Spray a13x9-inch baking pan with baking spray. Set aside.
Cake: In a large bowl use a whisk to sift together flour, sugar, baking powder, baking soda and salt.
In a separate medium bowl whisk together the milk, sour cream, melted butter, vanilla extract and eggs.
Add the wet ingredient mixture to the sifted dry ingredients stirring together by hand until fully combined. (You can also use an electric mixer on medium speed.) Pour the batter into the baking pan.
Cinnamon Swirl: Combine softened butter, brown sugar, flour and cinnamon together in a medium bowl until smooth. Drop tablespoon dollops over the batter in the baking pan. Use the tip of a knife to swirl the cinnamon mixture into the cake batter to create a marble effect.
Transfer to the oven and bake for 30-40 minutes or until the top is golden brown and a toothpick inserted into the center of the cake portion comes back clean. Let the cake cool for 5-10 minutes on a wire rack while you make the glaze.
Vanilla Glaze: In a small bowl stir together the powdered sugar, cream and vanilla extract until smooth. Drizzle over warm cake.
Cut into squares and enjoy warm.