1. Prepare Oven and Pan:

• Preheat your oven to 425°F (220°C).
• Grease an 11×7-inch baking dish. Lining it with parchment paper, leaving an overhang on two sides for easy lifting, is highly recommended. If using parchment, lightly grease the parchment too.

2. Make and Bake the Crust:

• In a medium mixing bowl, combine 1 cup of the all-purpose flour, the ½ cup of softened butter, and 1 tablespoon of white sugar.
• Use a fork, a pastry cutter, or your clean fingertips to mix and cut the butter into the dry ingredients until the mixture becomes crumbly.
• Press this crumbly mixture firmly and evenly into the bottom of the prepared 11×7-inch baking dish.
• Bake the crust in the preheated 425°F oven for about 10 minutes, or until it just turns lightly golden.
• Once done, remove the crust from the oven and set it aside. Reduce the oven temperature to 350°F (175°C).

3. Prepare the Rhubarb Filling and Layer:

• In the same mixing bowl (no need to wash), stir together 1 cup of white sugar and the remaining ¼ cup of all-purpose flour.
• Add the 4 cups of chopped fresh rhubarb to the sugar-flour mixture and stir well to ensure all the rhubarb pieces are evenly coated. (If you had lemon juice, it would be added here).
• Evenly spread this rhubarb mixture over the top of the pre-baked crust in the dish.

4. Make and Layer the Cheesecake Mixture:

• Ensure the cream cheese is fully softened to room temperature.
• In a medium bowl, using an electric mixer (or whisking vigorously by hand), beat together the softened cream cheese, ½ cup of white sugar, and the 1 large egg until completely smooth and creamy. (If you had vanilla, it would be added here).
• Carefully spoon or pour this creamy cheesecake mixture over the rhubarb layer, spreading it as evenly as possible.

5. Bake the Bars:

• Place the baking dish in the oven, now preheated to 350°F (175°C).
• Bake for about 35 minutes. The cheesecake layer should look set (it might have a very slight jiggle in the center), and the rhubarb filling underneath should be bubbling around the edges.

6. Make and Apply Sour Cream Topping:

• While the bars bake (during the last few minutes), prepare the sour cream topping. In a small bowl, mix the ½ cup of sour cream and 1 tablespoon of white sugar together until smooth.
• As soon as the bars come out of the oven (while they are still warm), carefully spread the prepared sour cream mixture evenly over the hot cheesecake layer.

7. Cool Completely:

• Place the pan on a wire cooling rack and let the bars cool completely at room temperature. This is very important for the layers to set properly.
• Once fully cooled, cover the pan loosely with plastic wrap and transfer to the refrigerator to chill for at least 2-3 hours, or preferably longer, before slicing.

8. Slice and Serve:

• Once thoroughly chilled, use the parchment paper overhangs (if used) to lift the entire block of bars out of the pan onto a cutting board.
• Use a large, sharp knife to cut into squares or rectangles. For the cleanest cuts, wipe the knife blade clean with a damp paper towel after each cut.
• Store any leftovers covered in the refrigerator. Enjoy this cool, refreshing treat!