1Preheat an oven to 325 degrees F (165 degrees C). Prepare a 9x9-inch baking dish with cooking spray.
2Mix together 1 cup of flour, 2 tablespoons of sugar, and the melted butter until well combined; pat the mixture into the bottom of the prepared baking dish.
3Bake the crust in the preheated oven until very lightly browned, about 25 minutes. Set aside to cool slightly. Increase oven heat to 350 degrees F (175 degrees C.)
4Stir together 1 1/4 cup of sugar, the rhubarb, 2 tablespoons flour, the milk, and beaten egg yolks until thoroughly combined; pour over the crust.
5Bake in the oven until set, 40 to 45 minutes. Serve warm.