Chop the strawberries into small bite size pieces then add them to a bowl with 1 tablespoon of granulated sugar. Cover the bowl and set aside for 1 hour. This is to remove the majority of water from the strawberries so your blondies don’t come out soggy.
Use a sieve to strain the strawberries over a small pot then set the pot with the liquid aside. Lay out some kitchen towel on a clean surface and place the strawberries on top. Place another kitchen towel on top of the strawberries then pat dry to remove the excess liquid.
Carefully scrape the strawberry pieces into a bowl, mix in the cornflour and set aside. Preheat the oven to gas mark 4/350oF/180oC/160oC fan and line an 8 x 8 inch (20 x 20cm) with baking paper.
To a microwaveable mixing bowl, add the butter and melt at 30 second increments. Once melted, add both sugars and mix well. Mix in the egg and vanilla extract then mix in the salt.
Fold in the flour then gently fold in the white chocolate and strawberries. Add the mixture to the prepared baking tin and use a palette knife to spread and smooth the mixture evenly in the tin.
Place the saucepan with the strawberry liquid onto a medium heat and cook for 4 minutes or until the sauce becomes jammy. Using a pastry brush, brush the strawberry sauce on top of the blondie mixture in the tin.
Bake in the middle of the oven for 40 minutes. Once baked, place the tin onto a cooling rack and allow to cool for 30 minutes then remove the bar from the tin and allow to completely cool on the cooling rack. Once cooled, cut into 16 bars and enjoy.