white chocolate on another sheet of parchment. Refrigerate until chocolate is firm but not brittle, about 15 minutes. Cut chocolate crosswise into 3/4-inch-wide strips. Refrigerate to refirm chocolate, about 15 minutes. Carefully arrange strips alternately around edges of cake, gently pressing into icing. Spoon reserved chocolate cream into pastry bag fitted with a no. 3 round tip. Pipe mixture into straight lines atop the cake. Dust lightly with cocoa;' refrigerate. Garnish with chocolate leaves. Bring to room temperature before serving.