In a small bowl whisk together the cocoa powder and the water until the cocoa powder is dissolved and let the mixture cool to room temperature. In a bowl whisk together the flour, the baking soda, and a pinch of salt. In another bowl with an electric mixer cream together the butter and the sugar and beat in the whole egg and the egg yolk, beating until the mixture is combined well. Beat in the cocoa mixture alternately with the flour mixture, beating well after each addition, divide the batter among 12 paper-lined 1/2-cup muffin tins, and bake the cupcakes in the middle of a preheated 350 degree oven for 25 to 30 minutes, or until a tester comes out clean. Turn the cupcakes out onto a rack and let them cool completely.
In another bowl combine the butterscotch chips and the cream, scalded, let the chips soften, and whisk the mixture until it is smooth. Let the icing cool completely, whisk it until it is fluffy, and spread it on the cupcakes. As an alternative, substitute semi-sweet chocolate chips for the butterscotch chips.
Recipe courtesy of Gourmet Magazine