Cream the butter and sugar together until light and fluffy. In a separate bowl, mix the flour and cocoa together. Alternate adding the flour mixture and egg into the sugar, beating well to fully incorporate after each addition.
Grease a 1 liter bowl (I used a small Pyrex), and place the pears, flat side down, in the bottom of the bowl. Pour the batter in on top and smooth. Cover the bowl with waxed paper, then aluminum foil.
Steam in a large stockpot for approximately 90 minutes. The top of the pudding should look like a firm cake. Let cool slightly in bowl to ensure a set, then turn out onto a plate. Spoon on chocolate sauce, and serve.