Preheat the oven to 340°F.
Lightly grease a 9-inch square baking pan.
Mix the milk and vinegar together and set aside to thicken.
Add the yogurt and oil to the milk mixture.
Sift in the flour, cocoa powder, baking powder, and sugar.
Gently mix until just combined.
Pour the batter into the prepared baking pan.
Combine the light brown sugar and cocoa powder for the sauce.
Sprinkle the sugar mixture over the cake batter.
Pour the boiling water over the top.
Bake for 30-35 minutes, or until the center is almost set.
Let it cool slightly before serving with ice cream. Enjoy!