Preheat the oven to 170°C / 150°C fan. Grease and line a square baking tin approx 7x7" - 8x8" in size.
In a large bowl, mix the melted butter and peanut butter.
Add the eggs, vanilla, brown sugar and caster sugar and beat until well mixed.
Add the almond milk and mix again.
Sieve in the flour and add the cornflour and xanthan gum. Gently fold in until just combined.
Sprinkle over your chocolate chips and gently mix again to combine.
Transfer the mixture to your baking tin and bake for approx 30 minutes. If the top starts to become too browned, cover loosely with foil. The blondies will be very gooey in the middle when first removed from the oven but will firm up as they cool.
Leave in the tin for 5 minutes before transferring to a wire rack to cool for at least 2 hours.
If adding extra white chocolate on top, melt this in a bowl in the microwave (in 30 second bursts to prevent burning). Use a small spoon or knife to drizzle the melted chocolate over the top of the blondies.
Cut your blondies into 12 and enjoy! These will keep well in an airtight container for up to 5 days.