Sift flour, baking soda, salt into a small bowl and set aside.
In a larger bowl, cream together butter and brown sugar until well-blended. I do this by hand with a wooden spoon.
butter and brown sugar
Add egg and continue to beat, by hand, until well-mixed.
Stir in vanilla.
Now, ALTERNATE between adding the 1 cup of milk and the flour/baking soda/salt mixture that you had set aside: Add about a 1/4 of the milk and stir well. Then add about 1/4 of the flour mixture, and stir well.
Continue until all is added to the batter.
Stir in chopped rhubarb.
rhubarb cake batter from scratch
Spoon into a sprayed (or greased and floured) 9 x 13 baking dish or cake pan.
ADDING THE CINNAMON-SUGAR TOPPING:
sugar and cinnamon
Mix the white sugar and cinnamon in a small bowl and mix well. Sprinkle over the batter until cake is entirely covered.
Shake the pan from side to side to evenly distribute the sugar if necessary.
rhubarb cake with sugar cinnamon topping
Bake at 350º F for 40 minutes (or until knife comes out clean).