This recipe originally came from my aunt and it's in our family cookbook.

1/2 cup butter
1 1/2 cups sugar
1 egg
1 cup buttermilk
1 teaspoon vanilla
1 teaspoon baking soda
1 pinch of salt
2 cups sifted flour
1 1/2 cups chopped rhubarb

Topping:
1/3 cup sugar
1 teaspoon cinnamon

Preheat oven to 350°F and grease a 9x13 pan.
Cream butter and sugar with eggs and vanilla until light and fluffy.
Sift flour, baking soda, and salt together.
Add flour mixture alternately with buttermilk; fold in rhubarb.
Pour into prepared pan.
Mix together topping ingredients and sprinkle evenly over batter.
Bake for 35 minutes or until toothpick inserted in center comes out clean.