Beat yogurt until smooth.
Add oil and mix well.
Add semolina, salt, and sugar and stir well. Cover and keep for 20 minutes.
Preheat oven to 180 degrees C. Grease and line one 8 inch round cake pan.
Add vanilla extract to the semolina mixture. Mix.
Add baking powder, baking soda, and grated apples. Stir to mix well.
At this stage, if the batter feels very thick, add warm milk to get the right consistency.
Pour the batter into the prepared pan. Arrange blackcurrants on top.
Bake for 35-40 minutes or until the top is firm to touch and a toothpick inserted in the center comes out clean.
Remove from the pan after 10 minutes. Cool on the rack.
Slice when cold.