Place the sugar in a large mixing bowl, and add the egg yolks. Whisk until smooth.
Add the baking powder and cornstarch and whisk again.
Add the yogurt and whisk until all the ingredients are well combined.
In another clean bowl, beat the egg whites until stiff peaks form.
Fold the whipped egg whites into the batter.
Add the chocolate chips and mix gently.
Pour the batter into an 8-inch cake pan lined with parchment paper.
Bake at 170°C/350°F for 1 hour. (fan assisted oven)
Dust with powdered sugar and serve.
TIP: A drastic drop in temperature can make the cake deflate. Let it cool gradually in the oven with the door slightly open.
Store the cake in the fridge, in an airtight container for up to 4 days.
