1. Grease 23 cm/9 inch round cake tin; line bottom of tin with non-stick baking parchment.
2. Preheat oven to 180C/350F/gas 4. In large bowl, with electric mixer, beat first 7 ingredients until blended, occasionally scraping bowl.
3. Spread mixture evening in tin. Bake for about 30-35 minutes or until skewer inserted in centre comes out clean. Cool in tin or on wire rack for 10 minutes. With palette knife, loosen cake from edge of tin; turn out on wire rack; peel off parchment. Cool completely.
4. Meanwhile, in small bowl over pan of gently simmering water, heat chocolate, stirring often, until melted and smooth. Pour on to 2 large baking sheets, spread evenly and make chocolate scrolls.
5. Make more chocolate scrolls with chocolate cake covering on second baking sheet. (Consistency of cake covering is very important. If it is too soft, it will not curl; if too hard, it will crumble. If too firm, leave it to stand at room temperature for a few minutes until soft enough to work with; if too soft, return to refrigerator.) Refrigerate scrolls until firm.
6. Make chocolate glaze.
7. Carefully brush away crumbs from cake. Place cake on wire rack over greaseproof paper.
8. Spoon chocolate glaze over top and side of cake (some glaze will drip on to greaseproof paper underneath).
9. Leave cake to stand at room temperature until glaze is firm, about 45 minutes.
10. Transfer cake to plate. Arrange chocolate scrolls on top and sift over icing sugar.
For the chocolate glaze
In small heavy saucepan over very low heat, heat 90g/3 oz plain chocolate, broken into pieces, 45g / 1 1/2 oz butter and 2 teaspoons golden syrup, stirring frequently, until melted and smooth. Remove from heat; stir frequently until glaze cools and thickens slightly
For the chocolate scrolls
Spread chocolate with palette knife, spread melted chocolate flavour cake covering over baking sheets to cover evenly. Refrigerate until firm but not brittle, about 10 minutes.
For the scrolls place 1 chocolate-covered baking sheet on damp cloth on work surface (damp cloth keeps baking sheet from moving while working). Using straight-edged knife or palette knife, push blade across chocolate to form, long thin scrolls.
Transfer scrolls with a cocktail stick to another baking sheet.