Put the raspberries in a saucepan with the water and icing sugar over a medium heat for 5-10 minutes until the mixture becomes quite thick and like jam. Press through a sieve to remove the pips and leave to cool.
Melt the butter and place in a bowl with the sugar then whisk in the egg.
Tip in the flour and white chocolate chips and use a metal spoon to fold the mixture together.
Grease and flour a tin and add the blondie mixture.
Drizzle the purée over the batter and use a skewer or the end of a spoon to gently swirl the mixture in. Push the raspberries into the mixture.
Bake at 180C/350F/Gas 5 for 30 to 40 minutes until the blondies are set.