Actually, from citrus, we need only the crust. So, cut them in half, squeeze the juice (or just carefully take out the contents)and put it on hold for a second.

Apple finely cut, sprinkle with lemon juice (2-3 tbsp), add the cinnamon, vanilla, chopped nuts and brown sugar (2-3 tsp). Gently mix and place in prepared citrus cups. I have 2 lemon and 4 orange, and you Vice versa).

Top each Cup sprinkle with more brown sugar to form a caramelized crust. I, as an experiment, two cups still sprinkled with oat flakes of fast preparation from "Mistral". Not too bad a result). Put into the oven for 20 minutes at 180 degrees. That's the whole process).