Rhubarb Coffee Cake

1 1/2 cups firmly packed brown sugar
1/2 cup shortening or margarine
1 cup buttermilk or sour milk
1 teaspoon vanilla extract
2 eggs
2 cups flour
1 teaspoon baking soda
1/4 teaspoon salt
2 teaspoon cinnamon
1 1/2 cups rhubarb, finely diced

Cream sugar and shortening; add in buttermilk, vanilla extract and eggs. Mix well. Add combined dry ingredients; beat all slowly and fold in rhubarb. Pour into a greased and floured 13 x 9-inch pan. Sprinkle on a mixture of 1/4 cup granulated sugar and 1 teaspoon cinnamon. Bake at 350 degrees F until done.