Use a 33×23cm baking tray. Line with baking paper. Preheat oven to 180°C.
Beat eggs, sugar, orange zest and juice until fluffy. Sift flour and baking powder over the egg mixture; fold in with a whisk.
Spread mixture evenly on tray; bake for 12–14 minutes or until golden brown. Remove from oven, turn out onto baking paper (leaving tray on top of sponge); cool.
Melt chocolate in a bowl over gently simmering water; cool. Whip cream until stiff. Gradually stir in chocolate, coffee and icing sugar. Place about 6 tbsp chocolate cream in a piping bag fitted with a star nozzle.
Remove tray and top sheet of paper from sponge. Spread three-quarters of chocolate cream over sponge. Using bottom sheet of baking paper to help keep the roll neat, roll up sponge; work from a long side.
Spread remaining chocolate cream over roll and pipe small rosettes on the top. Dust with the cocoa powder and decorate with chocolate flowers and leaves.