Found this on Dixie's Kitchen website. Even though there's no top crust it appears to form one during baking.
Ingredients
2 cups all-purpose flour
3/4 cup powdered sugar
1 cup butter
4 eggs
2 cups sugar
1/2 cup flour
1 1/2 teaspoons salt
4 cups rhubarb, finely chopped
Instructions
Combine 2 cups flour, powdered sugar and butter. Mix well and press into a greased 9″ x 13″ pan. Bake at 350 degrees until golden brown, 10 to 15 minutes.
Beat eggs, sugar, 1/2 cup flour and salt until well blended. Add rhubarb; mix. Spoon mixture onto baked crust. Bake at 350 degrees for 45 minutes more. Cool and cut into bars.
Note: I think sprinkling granulated sugar on top of this would be good. She suggested serving them warm with ice cream or whipped cream.