Pre-heat oven to 180C. Chop rhubarb into 2.5cm lengths and toss with 100g of the sugar. Arrange over the base of a large ovenproof dish. Finely grate the orange over the rhubarb and squeeze over the juice, mix well.
Cream together the sugar and butter with an electric mixer until pale and fluffy.
Add the eggs one at a time and mix in.
Pour in the vanilla extract and mix.
Sift together flour and baking powder and gradually add to the the wet mixture.
Slowly pour in the milk and mix to a smooth cake batter. N.B. Annie Bell suggests you pop all the sponge ingredients in at once and blitz in the processor.
Pour and scrape the cake mixture on top of the rhubarb and smooth over the top.
Sprinkle over the sugar mixed with cinnamon for a crunchy topping and bake for 45 minutes.
Serve with plenty of Avonmore Custard or Dessert Cream.