Boil a kettle. In a small bowl, mix flaxseed with boiling hot water and set aside. This will create a flaxseed 'egg'.
In a separate bowl mix together both sugars, flour, salt and cornstarch.
Melt butter (either in a microwave or in a small pan - careful not to burn). Add vanilla extract and stir well.
Then add the flaxseed 'egg' to the butter mixture. Stir well.
Slowly pour your wet mixture over your dry ingredients. Mix until combined and no more flour specks can be seen.
Chop up the hazelnuts. Roast hazelnuts in a small non-stick pan until golden around the edges (2-3 minutes). Do not use any oil.
Chop up white chocolate.
Add hazelnuts and white chocolate to your batter. Gently fold them in, making sure not to overmix the batter.
Pour the mixture into a lined baking tray.
Bake at 180°C/356°F for 25-20 minutes (fan oven setting*).
Melt white chocolate (in a microwave or over a water bath) and drizzle over the blondie in quick diagonal motions.
Allow to cool before slicing.