Preheat your oven to 180C/160C Fan, and grease and line a 9x9inch Square Tin - leave to the side for now.
Melt the Butter in the microwave, or in a pan, and stir till smooth. Leave to cool slightly on the side.
Using an electric whisk/stand mixer, whisk together the Eggs and Caster Sugar for a good 3-4 minutes or longer, until it has become much thicker, mousse like, paler, and basically doubled in volume.
You will know its done when when you lift the whisk up, it will leave a trail on the top of the mixture for a couple of seconds before sinking back in.
Once whisked up, continue whisking but gradually pour in the butter. Don't pour it in too quickly or the mixture will split.
Once all whisked in. Add in the Flour and Lemon Zest and fold together. Add in the White Chocolate Chips, and half of the Blueberries and fold again.
Pour into the tin, and sprinkle on the rest of the Blueberries.
Bake in the oven for 35-45 minutes, or until its baked through. Sometimes it can take longer due to some ovens, and if you have actually whisked it up enough in the first place.
Once baked, leave to cool in the tin.
Once cooled, remove from the tin and drizzle over the 100g of melted chocolate for decoration, and some sprinkles to boot! Leave to set and but up into your squares.
Sometimes Brownies & Blondies and such can take a while to bake, for some random reason… so if at 35-45 minutes yours isn’t baked through fully, cover the top with foil to prevent burning and continue to bake till done!
I have never tried this with frozen berries, and I’m not sure if it would work or not because of the moisture content. However, I seriously would recommend to NOT add any more blueberries then specified as moisture is released from normal blueberries as well, and the Blondies might not bake very well with any more!
The white chocolate chunks are entirely optional, but I just love the flavours of white chocolate and lemon together!