When I was a kid, I didn't like olives at all. Granted, there weren't any fancy olive bars back then (or if there were, they didn't have them in The Sticks).
Then, a few years ago, I was dating a guy who put olives in his chili. Because I like to challenge my own assumptions, I tried it (in this particular case they were green olives) and was surprised to find that I actually liked it! From that point on, I was much more open to olive tasting opportunities.
Then, a year ago, I went to a tapas restaurant with my brother and his wife. I loved the mild tasting olives they had in the olive plate. I remembered the name: "castelvetrano." However they proved very hard to find! One thing that hampered my search, I'll admit, is the fact that I avoid going into Whole Foods. I think it's fabulous and fun to go into, but that's the trouble. I end up spending MUCH more than I intend to every time I go there. Then, a few months ago, I saw that a neighborhood restaurant had a market area and an olive bar. Wonder of wonders, they had Castelvetrano olives! Last week, I used the excuse that I needed to take some offering to a dinner meeting and bought a tub of olives. Of course, I made sure a generous proportion of that was Castelvetrano olives. They are as good as I remember. They are buttery and salty and a bit sweet. It's funny that part of my brain still says "ewww olives, yucky!" but another (apparently louder) part that says "More Please!"
I found a couple of sites that talk about the Castelvetrano olive:
One, a blog post: it has some good pictures and descriptions
Two, an article about their new popularity: again, this has some great information.