Preheat the oven to 160c
Grease and line three shallow 9 inch baking tins with baking paper
Finely chop the white chocolate and set a side
Break the raspberries in to small chunks by hand and place in a bowl.
cut the rhubarb in to small chunks and place in a bowl with 1 tsp flour and 1 tsp sugar.
Cream the butter and sugar together until very pale and fluffy, at least 5 minutes.
Use a spatula to scrape the bowl, then add the first egg and beat for 2 minutes, then scrape the bowl again and add the next egg. Continue this process with the next two eggs. Then add the vanilla.
Sift in the flour and salt and fold in using a spatula, then fold in the raspberries, rhubarb and white chocolate.
Add the milk to loosen the batter, fold in and then separate the mixture between the tins and level out.
Bake in the centre of the oven to 20-22 minutes.
check cakes are done by inserting a knife into the centre. If it comes out clean they are ready.
Leave to cool in the tins for 15 minutes. The gently remove the cake layers from the tins and peel off the baking paper and place on a cooling rack until completely cool.