dessert: rhubarb cake

Here's a REALLY good rhubarb cake recipe that I got from my SIL. I'm not sure where she got the recipe, though. This cake is SOOOO yummy! I froze rhubarb this summer so I could make the cake any time of the year.
Rhubarb Cake
Ingredients:
1 ½ cups brown sugar1 egg or egg substitute1 tsp. vanilla½ cup butter, margarine, or unsweetened applesauce2 cups all-purpose flour1 tsp. baking powder1 tsp. baking soda ½ tsp. salt1 cup "sour milk "1-1/2 cups diced rhubarb, rinsedTopping:½ cup brown sugar1 tsp. cinnamonDirections:Preheat the oven to 350ºF and grease a baking pan with butter or vegetable oil (approx. 8x12)
Prepare the "sour milk" by adding 2 tbs. vinegar or lemon juice and milk (or non-dairy substitute) to measure out to 1 cup, let sit up to 5 minutes
Cream together egg (or substitute), brown sugar, and vanilla in a large bowl.
Beat in butter or other ingredient used.
In a separate medium bowl, combine flour, baking soda, baking powder, and salt.
Add the dry mixture and the "sour milk" alternately to the sugar mixture.
Fold the chopped Rhubarb into the mixture.
Pour into baking pan.
Mix the ½ cup brown sugar with 1 tsp. cinnamon and spread atop the unbaked cake.
Bake at 350ºC for 40 minutes or until the cake becomes a nice golden brown