Preheat oven to 350 degrees F.
Spray a 9 x 13-inch baking dish with nonstick cooking spray.
With a mixer, cream 1 stick of butter and 1/2 cup sugar. Add one egg, and one egg yolk and mix until smooth. (Reserve the extra egg white for later.)
In a small bowl, mix together 2 cups flour, 1/2 teaspoon salt and 1/2 teaspoon baking powder. In a separate bowl, mix together 2 Tablespoons milk and 1 teaspoon vanilla.
Add flour mixture alternately with milk mixture to the mixer, blending just until a dough forms.
Press into the prepared 9 x 13-inch pan; set aside.
Beat the leftover egg white until white and foamy. Spread over dough.
Spread rhubarb that has been washed and diced over the egg white.
Sprinkle jello mix evenly over rhubarb.
Mix together remaining 1 cup flour, 1 1/2 cups sugar and 1 stick butter until crumbly. Sprinkle over rhubarb.
Bake for 40-45 minutes on bottom shelf until bubbly.