Pre-heat your oven to 175°C and prepare an 8×8 inch baking pan, lining and greasing it with parchment paper. I like to place the parchment paper such that it is pressed against the sides of the pan, with some excess parchment hanging out over the edges. This ‘parchment sling’ makes it easier to remove the blondies later!
Sift the flour into a bowl. Whisk in the baking powder, cornflour and sea salt and mix well. Set aside.
Once the melted butter has cooled, beat the brown sugar and melted butter together until it is well mixed and fluffy.
Beat in the egg, egg yolk and vanilla extract until the mixture is light and evenly mixed.
Stir in the dry ingredients, gently folding them in until no visible streaks of flour remain.
Gently fold in ¾ cup of chocolate chips, reserving the rest to add in later.
Pour the batter into your prepared tin and press down gently with a rubber spatula/ offset spatula. Add the remaining chocolate chips and gently press down.
Pop the blondies into bake for 17 – 22 minutes (baking times vary from oven to oven). Remove them from the oven when they look *almost done*. The edges will have browned, but the centre will look a tad underdone (with a slight wobble). Be careful not to over-bake in the oven, as if you do, your blondies will be less moist, instead becoming hard. No one wants over-baked blondies!