As an Istanbul traveler, I think it is impossible for anyone to miss Ortaköy, since all guides mention the most famous attractions. However, since you are reading this to experience something more local, take half an hour to wander around the backstreets of Ortaköy, which represents a typical old style colorful neighborhood with a taste of the old. The small streets that cross Dereboyu Street are great to check some shops, try a bit of local tastes or just feel the traditional Ortaköy with the locals.
After wandering on the seaside, now it is time to cross Muallim Naci Street and walk onto Dereboyu Street. This is one of my favorite streets since I can find anything that I need here. First recommendation for lunch is Bizce Kuru (Dereboyu Street, Nr: 52, on the right hand side). They serve the best beans, of course with rice. Beans are cooked very slowly and the butter adds to the taste and smell.
You can also have yoghurt or cacik (diluted yoghurt with cucumbers) on the side. And finally try their rice pudding, just tell the waiter to add everything! Then your rice pudding comes with honey and nuts on top. By the way, having beans in the summer time when the weather is hot and humid can be exhausting afterwards.