Put the butter and the chopped chocolate into a bowl that sits over a pot of boiling water. The steam will gently melt the chocolate so that you can easily mix it with the butter.
In a second bowl, beat the egg and sugar until frothy. Add the cocoa powder along with the flour and beat until smooth. Pour in the melted butter and chocolate mixture and mix well.
Transfer the mixture to a greased, six-cup muffin pan and bake for 7 minutes at 425°F.
To serve, place the cakes upside down on a plate and sprinkle with powdered sugar. Now sit back and enjoy. That warm chocolate river flowing from the center of the cake wants nothing more than to make your taste buds happy!
