Bittman's Brownies with Frosting: A Lunchtime Request

I felt like baking this afternoon.  I said so at lunch, and Michael said he wanted to help.  We decided on brownies, WITH FROSTING this time, so once again I pulled out Bittman.  This time we added his Chocolate Buttercream Frosting for the top.

Yummy.  A chocolatey mess.  Michael loved them.  Goal accomplished.