Pre heat your oven to 160C Fan/350F/Gas Mark 4, and grease and line a 9" square traybake tin
Melt the butter with the golden caster sugar in a pan on a low heat
Once the butter has melted, take the pan off the heat and add the white chocolate. Leave it for about 5 minutes, then stir together until the white chocolate is fully melted. Don't worry if it looks a bit lumpy or separated
Transfer the mixture to a mixing bowl at this point if you like. Add the eggs and lemon zest to the mixture, and whisk to combine
Add the plain flour, blueberries and white chocolate chips, and mix them in, then pour the mixture into the lined tin
Bake the blondies for 30-35 minutes, or until they are golden brown all over. Using a skewer inserted in the centre doesn’t give a clear indication that they are done because blondies are meant to be gooey and almost a little under cooked. Blondies are the white chocolate version of brownies and they are not like cake. They will also set more as they cool down
Leave to cool in the tin, then put them in the fridge for a couple of hours. Then remove from the tin and slice
Make an icing by mixing together the icing sugar and lemon juice. Add the lemon juice slowly as you may not need it all
Drizzle the icing all over the blondies, I used a piping bag with the end snipped off, or you can use a spoon
Store leftovers in an airtight container in a cool place and eat within 3 days