Rhubarb Shortbread Bars

Preheat oven to 350 degrees F (175 degrees C).

Mix 1 cup flour, butter, and confectioners' sugar together in a bowl; pack the mixture firmly into the bottom of a 9-inch square baking dish.

Bake in preheated oven until the crust hardens slightly and is very fragrant, but not yet browned, about 15 minutes.

Whisk brown sugar, eggs, white sugar, 1/4 cup flour, and salt together in a bowl until completely smooth; add rhubarb and stir to coat.

Pour the rhubarb mixture over the crust.

Bake in oven until the rhubarb mixture sets, about 40 minutes; cool at least 10 minutes before cutting into bars.