Preheat oven: 180°C / 160°C (fan) / Gas Mark 4 / 350°F
If you haven’t already, peel, core and chop the apples into small pieces (roughly ¼ inch size).
Stir 2 tablespoon (20g) of brown sugar into the apple pieces and set aside.
In a large heatproof bowl, melt the butter for 30-50secs in the microwave and beat in the remaining sugar (200g) until smooth and thickened.
Thoroughly beat in the egg, vanilla extract and salt.
Sieve in the flour and cornstarch, adding the cinnamon and nutmeg, stirring until just combined.
Gently fold in the apple pieces until spread through the batter.
Pour the blondie mix into a greased and lined 8-inch square pan, smoothing the top gently.
Bake for 25-30mins until the top is lightly golden and there is only a slight wobble in the middle.
Allow blondies to cool fully in the tin before removing, then cut and enjoy! Or serve warm with ice cream, cream or custard.