To a saucepan, add the raspberries, sugar and lemon juice and place on a medium to high heat. Stir continuously until the raspberry sauce thicken. It will turn into a thick syrup and go a deep red when ready. Set aside to cool. Once cooled it will thicken further to become jam.
Preheat the oven to gas mark 3/325oF/160oC/140oC fan and line a small 1lb loaf tin with parchment paper then set aside. To a bowl, add and cream together the butter, oil and sugar. If using a stand mixer, use a paddle attachment. Mix in the vanilla and egg then the yoghurt and milk. Add in the salt and bicarbonate soda then add the self-raising flour and fully combine.
Remove ⅓ of the batter and add to another bowl. To that bowl add the raspberry jam and mix until the jam has fully combined with the batter. Optionally, you can add a few drops of pink food colouring to brighten the batter further.
Add ¼ cup of the vanilla batter to the tin then add ¼ cup of the raspberry batter. Place the batter in random sections of the tin to create a marble effect. Repeat the process until all the batter is used up then use a skewer to mix the batter in a circular motion to make the swirls. Bake in the oven for 55 – 60 minutes then place the tin on a cooling rack to cool in the tin for 1 - 2 hours. Once cooled, slice and serve.