Preheat the oven to 350 °F. Grease and flour a 9x13 baking dish.
Make the sour milk by combining the 1 cup of milk with 1 tablespoon of white vinegar. Set aside.
Cake
In the bowl of an electric mixer, combine the shortening, brown sugar, and salt together. Cream together.
Add the flour and baking soda. Mix together until combined.
Add the sour milk and the egg. Mix together until combined. Batter will resemble creamy peanut butter. Using a spatula, fold in the chopped rhubarb.
Add the batter to a prepared baking dish, smoothing it out until even.
Topping
In a small bowl, combine the sugar, nuts, and cinnamon. Sprinkle the topping evenly over the cake batter.
Bake
Bake for 45 to 50 minutes or until a toothpick inserted into the cake comes out with just a few crumbs. Cool on a baking rack.
Notes
Sour milk is an old-fashioned term for Buttermilk. If you choose, you can replace the 1 cup of milk and the white vinegar with 1 cup of buttermilk.Cake can be served with a dollop of whipped topping.
This recipe was calculated using the exact brands and measurements I used to make this recipe. If you are following a strict diet please note changing anything will cause the nutritional info to change. My calculations are intended as a guide only.