Preheat oven to 425 degrees F (220 degrees C). Grease an 11x7-inch baking dish.
In a bowl, mix together 1 cup flour, the softened butter, and 1 tablespoon sugar until well combined; press into the bottom of the prepared baking dish.
Bake the crust in the preheated oven until it starts to brown, about 10 minutes. Remove the crust. Reduce oven heat to 350 degrees F (175 degrees C).
Using the same bowl, thoroughly mix 1 cup sugar with 1/4 cup flour; stir in the rhubarb and toss to coat. Spread the rhubarb mixture over the baked crust. Using the same bowl, mash the cream cheese, 1/2 cup of sugar, and the egg until the mixture is creamy; spread over the rhubarb.
Bake in the oven until the rhubarb is bubbling and the topping is set, about 35 minutes.
In the same bowl, mix sour cream with 1 tablespoon of sugar; spread over the hot dessert. Allow to cool completely before cutting into bars. Refrigerate leftovers.