Preheat the oven to 350 degrees F (175 degrees C).
Make crust: Mix together flour, butter, and confectioners' sugar in a bowl; pack firmly into the bottom of a 9-inch square baking dish.
Bake in the preheated oven until crust hardens slightly and is very fragrant, but not yet browned, about 15 minutes.
Make filling: Whisk together brown sugar, eggs, white sugar, flour, and salt in a bowl until completely smooth; stir in rhubarb to coat. Pour rhubarb mixture over crust.
Bake in the oven until rhubarb mixture sets, about 40 minutes. Cool at least 10 minutes before cutting into bars.
