Combine 0.75 cup sugar and corn starch in medium sauce. Stir in rhubarb. Cook and stir over medium heat until mixture comes to a boil and thickens. Cool and set aside. Stir together milk and vinegar and set aside. Combine flour and remaining 0.75 cup sugar. Cut in butter until mixture is crumbly and set half cup of mixture aside. To remainder add baking powder, baking soda and nuts. Combine egg and milk mixture and add to dry ingredients, stir until just moistened. Spread two third of the batter over the bottom and sides of a buttered 23 cm spring form pan. Spoon rhubarb filling over batter. Drop remaining batter over rhubarb by spoonful, sprinkle with reserved streussel mixture. Bake in preheated 180ºC oven 50 minutes.