Preheat the oven to 210°C.
Mix Greek yogurt, cream cheese, and erythritol together.
Add eggs and vanilla extract, then mix well.
Sift in cocoa powder and corn starch, and mix.
Pour the batter into a pan and top with chocolate.
Bake in a 210°C oven for 25 minutes.
Let cool, then refrigerate for at least 3 hours to set.