In a medium saucepan combine sugar and cornstarch. Stir in rhubarb.
Cook and stir over medium heat, until mixture comes to a boil and thickens. Remove from heat and cool.
Combine milk and lemon juice. Set aside.
Combine flour and sugar. Cut in butter until mixture is crumbly ( a food processor is great for this). Remove 1/2 cup of this mixture and set it aside to use for topping.
To the remaining flour mixture add baking powder, baking soda, and walnuts.
Combine egg with milk mixture. Add to the dry ingredients and stir or process until just moistened.
Spread 2/3 of the batter over the bottom and part way up the sides of a greased 9 inch springform pan. Spoon the rhubarb filling over this. Drop the remaining batter by spoonfuls over the filling. Sprinkle with reserved crumb mixture.
Bake at 350 degrees for 50 minutes.
NOTE: 3/4 cup of buttermilk can be used in place of the milk. Omit lemon juice.
Printed from https://nowyourecookingrecipes.com/rhubarb-streusel-coffee-cake/