Grease a 13 x 9" cake pan. Preheat oven to 350. Beat butter and sugar in a bowl until smooth. Beat in the eggs, stir in sour cream and vanilla. Then add flour, baking soda and salt, fold into the creamy mixture, stir in rhubarb, then pour into cake pan.
Mix all topping ingredients in a bowl until crumbly, sprinkle over top of rhubarb mixture. Bake 35 minutes or until knife inserted into cake comes out clean. Serve warm, refrigerate leftovers. ENJOY!