From The Combes Family Inn, Ludlow, VT
In a bowl, beat sour cream and egg. Add sugar, flour, salt, and vanilla extract and mix until smooth. Stir in rhubarb. Pour into an 8-inch-square pan.
In another bowl, mix topping ingredients until crumbly. Sprinkle over the top of the rhubarb mixture. Bake 35 to 45 minutes. Serve with ice cream.