Pour the yoghurt into a small dish, cover and chill. Rinse out and dry the yoghurt pot, use as a measuring cup. Line the base of the springform pan (approx. 26 cm in diameter) with baking paper, grease the sides.
Break the chocolate into pieces, place in a thin-sided bowl. Suspend the bowl over a gently simmering bain-marie, ensuring that the bowl does not touch the water. Melt the chocolate and stir until smooth.
Cut the butter into pieces, place the butter, eggs, sugar and salt in a bowl.Mix using the whisk on a mixer until the mixture becomes lighter in colour.
Combine the almonds, breadcrumbs and baking powder, mix into the egg mixture.
Mix in the reserved yoghurt and melted chocolate. Transfer the batter to the prepared tin, smooth down.
Approx. 45 mins. in the lower half of an oven preheated to 180°C. Remove from the oven, allow to cool slightly, remove the tin frame, slide the cake onto a cooling rack and leave to cool completely. Cut out a piece and position it as a fin.
Warm the cream, break the chocolate into pieces, add to the cream, melt, stir until smooth, pour over the cake. Place Smarties on the cake as fish scales, chill for approx. 1 hr.