Pre-heat oven to 350F and lightly brush a 0.5qt mini dutch oven (or a 5" ramekin / cake pan) with butter
To make the cake, add the oil, yogurt and 2 tablespoon boiling water to a bowl, and whisk until combined. Whisk in the sugar
Sift in the flour, cocoa powder, baking powder, baking soda, and salt. Gently fold until the dry ingredients are just combined
Pour the batter into the prepared pan
In a separate little bowl, stir together the granulated sugar, brown sugar and cocoa powder for the hot fudge until no lumps remain. Sprinkle this mixture over the cake batter in the pan
Carefully pour over the ⅓ cup of boiling water on top of the sugar and cocoa mixture
Transfer the pan to the pre-heated oven and bake for ~20 minutes until the cake looks done on top. If in doubt, lean towards underbaking vs overbaking as you want a good amount of fudge sauce on the bottom
Serve the cake warm straight from the pan! Optionally, you can scoop some plain, cold whipped cream or ice cream on top
