Preheat the oven to 160°C fan and line a 9-inch square tin with parchment paper.
In a large bowl, mix the melted butter with both sugars until fully combined.
Add the eggs and lemon zest, then mix until smooth.
Fold in the flour, cornflour, and white chocolate chips.
Gently fold in the blueberries, then spread the batter evenly into the tin.
Bake for 25–30 minutes until lightly golden with a slight wobble in the center.
Allow the Lemon and Blueberry Blondies to cool completely in the tin.
Drizzle with melted white chocolate, sprinkle with lemon zest, chill for 2–3 hours, then slice.