Pour the yoghurt into a bowl, add the baking soda to it. Leave it aside to effervesce. Then add the sugar, while stirring well.
Melt the butter and add it to the mixture, along with the sifted flour. You're going to get a thick dough.
I used an 8″ (20 cm) per side square tray, smeared with oil and sprinkled with flour. Pour the prepared mixture into it, even it out on top.
Distribute the fig jam randomly on top and press.
Put in the oven and bake until ready, checking to see if it's ready with a skewer.
Leave to cool and then cut it.