Preheat oven to 300 degrees F. Grease a 9x13-inch baking pan; set aside. In a small bowl, combine the 1/2 c. sugar with the 1 tsp. cinnamon; set aside. In a large bowl, using an electric mixer, cream the butter and 3 c. sugar for 3 minutes on medium speed. Add the milk, eggs, and vanilla; mix until just combined.
Add the salt and baking soda. Mix for 3 additional minutes. Add the applesauce and mix for an additional 2 minutes. Add the flour; mix until fully blended (DO NOT OVERMIX).
Pour the batter into the prepared pan. Sprinkle the cinnamon-sugar mixture over the batter. Bake for 75-90 minutes or until a toothpick inserted into the center comes out dry. Cool completely on a wire rack.