Preheat the oven to 170C and line a 2lb loaf tin with baking parchment. Make sure there’s enough baking parchment so that you can pull the cake out using the parchment for handles. Put to one side.
Mix the egg and sugar in a large bowl. Add the oil and stir. Add the vanilla and yogurt and stir again. Finally mix together the flour and baking soda and fold into the cake mixture until combined.
Carefully fold three-quarters of the raspberries into the cake mix, and spoon two-thirds of the mixture into the prepared baking tin. Place the rest of the raspberries on top of the cake mix, and spoon the remaining cake mix on top (this helps to prevent the raspberries from sinking)
Place in the oven to cook for 50-70 minutes - until an inserted skewer comes out clean. Check every 5-10 minutes after the first 50 minutes. If the cake is looking too brown, you can cover with aluminium foil.
Once cooked, take the cake out of the oven and leave to cool in the tin for 10 minutes then remove from tin and allow to cool further on a cooling rack.
Drizzle melted chocolate over the top before serving.