1.Preheat oven to 200°C. Grease oven tray. Trace eight 7cm hearts onto a piece of baking paper to use as a guide. Line tray with paper.
2.Combine butter and water in medium saucepan; bring to the boil. Add sifted flour and cocoa, then beat with wooden spoon over high heat until mixture comes away from base and side of pan to form a smooth ball. Transfer mixture to a small bowl. Beat in eggs, one at a time, with electric mixer until mixture becomes glossy.
3.Spoon mixture into piping bag fitted with a 5mm plain tube. Pipe half of the mixture into eight hearts on tray, using paper as a guide. Pipe remaining mixture directly on top of previous hearts.
4.Bake hearts 7 minutes.
5.Reduce oven to180°C; bake a further 10 minutes or until crisp. Remove from oven. Using serrated knife, split hearts in half, return to trays. Bake about 10 minutes or until dried out.
6.Meanwhile, to make mocha cream, dissolve coffee in the hot water; cool. Beat cream, sifted icing sugar and coffee mixture in small bowl with electric mixer until firm peaks form.
7.Place half of the hearts, top-side up, on a wire rack over tray. Spread with chocolate. Leave to set at room temperature.
8.Fill remaining hearts with mocha cream and top with chocolate coated hearts.