Serves: 32 cookies1) Preheat the oven to 140C/Gas 4. Brush 2 baking sheets very lightly with oil.
2) Sift the flour, bicarbonate of soda, baking powder and salt into a medium bowl.
3) Whisk the buttermilk and vanilla together in a liquid measuring cup. Set aside.
4) Beat the butter in a large bowl with an electric mixer until smooth. Gradually add the sugar and continue to beat at high speed until light and fluffy, about 5 mins. Add the eggs and yolks, 1 at a time, beating well after each addition. At low speed, add the dry ingredients in 3 parts, alternating with the wet in 2 parts, beginning and ending with the dry to make a smooth batter.
5) Evenly mound 2 tbsp batter per cookie onto the prepared cookie sheets, spacing them about 5cm apart. (A small cookie scoop or ice cream scoop is ideal for this.) Bake until the cookies are golden brown around the edges, 12 to 15 mins. Transfer cookies to rack and cool completely.
6) For the chocolate icing: Put the chocolate in a medium heatproof bowl. Bring the cream to a boil in a small saucepan; pour over the chocolate. Shake the bowl gently so cream settles around the chocolate; set aside until the chocolate melts, about 5 mins. Whisk until smooth, taking care not to incorporate too many air bubbles. Fill a pastry bag fitted with a small tip with about half of the chocolate icing.
7) For the white icing: Whisk the icing sugar, golden syrup, lemon juice and warm water together to make a smooth icing. Fill a pastry bag fitted with a small tip with about a quarter of the icing.
8) For making tuxedo cookies: Set the cookies on a rack over a rimmed cookie sheet. Pour the white glaze over the whole cookie to cover; set aside to dry. Pipe a bowtie and tuxedo lapel with the chocolate icing.
9) For a little black dress and pearls: Pipe an outline of a woman's dress with the dark chocolate and fill in with more icing. Pipe white icing pearls around the top of the cookie. Add silver dragees or candy pearls to dress up, if desired.
10) Let cookies dry completely, about 20 mins. Serve. Store cookies in a tightly sealed container for up to 2 days.