1. Preheat oven at 180 degree C or 350 degree F.
2. In a large mixing bowl, add flour, cocoa, baking powder, baking soda, and sugar. Mix.
3. Pour beaten egg, milk, and olive oil in it. Mix to incorporate.
4. Drop raisins and hazelnuts. Fold to spread evenly.
5. Grease a baking tin, and pour the mixture in it.
6. Pop it in oven, and bake for 50-60 minutes.
7. Allow it to cool in the pan for 15-20 minutes.
8. Transfer it on a plate, and let it cool completely for about 2-3 hours or place it in refrigerator for about 45 minutes.
9. Spread chocolate topping, place it in refrigerator for 15 minutes, cut in slices and serve immediately.