Self-saucing moist chocolate cake. A layer of gooey chocolate pudding forms on the bottom as it bakes. Serve with ice cream or whipped cream. Or just stick your face in it.
Preheat oven to 350ºF and set a small pot or kettle of water to boil. Butter an 8x8" baking dish.
In a large bowl, whisk together flour, sugar, cocoa powder, baking powder and salt. In a separate bowl, whisk together milk, melted butter, sour cream and vanilla. Pour the wet ingredients into the dry and fold together until just combined (don't over-mix). Spread evenly into prepared baking dish.
Combine sugar and cocoa for topping and sprinkle evenly over cake batter. Pour boiling water over top and immediately transfer to the oven. Bake for about 50 minutes, or until top is a bit springy when gently pressed near the centre, but still has a bit of wobble. Let stand 15 minutes before serving (the middle will sink, this is normal and part of the delicious process).