Preheat the oven to 325°F. Lightly grease a 9" x 13" pan., To make the cake: In a large mixing bowl, beat together the butter, oil, sugar, vanilla, baking powder, baking soda, and salt until smooth., Beat in the eggs., Stir in the sour cream, buttermilk, or yogurt alternately with the flour. (See "tips," below for more details on this step, if needed.), Add the cocoa and espresso powder, mixing until smooth., Fold in the zucchini and chocolate chips. Spoon the batter into the prepared pan., Bake the cake for 40 to 45 minutes, until the top springs back lightly when touched, and it seems set. A toothpick or paring knife inserted into the center should come out clean when done., Remove the cake from the oven and cool in the pan on a wire rack., To ice the cake: In the microwave or on the stovetop, combine the chocolate chips and half-and-half, heating until the chocolate softens. Stir to melt the chocolate, and spread over the completely cooled cake., Storage information: Store leftover cake, well covered, at room temperature for several days; freeze for longer storage.