Heat oven to 180 C/( 350 F) Gas Mark 4. Butter two 18cm 9 7 in) sandwich tins and line with non-stick baking paper.
In a large bowl or electric food mixer, cream the butter and add the caster sugar and beat until light and fluffy. Add the eggs one by one beating all the time. Finally sift in the flour and baking powder and gently fold in along with the milk to incorporate.
Divide the mixture between the tins, smooth the surface with the back of a spoon.
Bake for about 20 – 25 mins until golden and the cake springs back when pressed.
Turn onto a wire rack and leave to cool completely
To prepare the rhubarb – wash and chop into 1in pieces and place over a gentle heat for approx 10 minutes until the rhubarb is soft. Increase the heat and reduce until thickened and the water has boiled off, taking care not to let it burn. Pour into a bowl and allow to cool completely. Fold in the whipped cream and spread over the bottom sponge. Sandwich both sponges together and sprinkle with icing or caster sugar.
Perfect for afternoon tea !