Set the oven to 170°C / 350°F with the fan.
Grease a square pan (I used a 15 cm / 6" pan) and line with baking paper
In a bowl, place the chocolate and butter.
In the microwave, in 30 second rounds, melt the chocolate with the butter until completely smooth.
Add sugar and salt to the bowl.
Mix well.
Add the eggs one at a time and mix well.
Sift in the cornstarch / potato starch and mix until batter is unified.
Pour the batter to the pan.
Tuck walnuts to the batter evenly.
Bake for 20 minutes.
Cool the brownies completely before cutting to squares.
Have a brownie and enjoy!