Step 1

For the base: Preheat the oven to 350 degrees F. Add the butter to a 9-by-13-inch baking dish and place in the oven while it preheats and melts.

Step 2

Mix the flour, sugar and cocoa powder in a bowl. Mix in the buttermilk and vanilla until a batter forms. Spoon the batter around the baking dish over the melted butter.

Step 3

For the topping: Top with the chocolate chunks, sugar and cocoa powder. Pour over the boiling water and, without stirring, bake until a nice crust forms, 40 to 45 minutes. Serve warm with cookies and cream ice cream.