Preheat oven to 350 degrees. Grease a 9x13 baking pan.

Beat together the shortening and brown sugar. Add egg and beat on medium until light and fluffy.

Mix together flour, baking soda and salt.

Alternate adding the flour mixture and the buttermilk, in about 3 additions each, while the mixture runs on stir or low.

Stir in the vanilla. Stir in the rhubarb.

Spread into prepared pan.

Mix together sugar and cinnamon. Sprinkle over the batter.

Bake for 45 to 50 minute until toothpick in the center comes out clean.

Cool before slicing and serving.