Amusingly only to me, this favorite food of mine is composed almost entirely of garnish. I do it mostly like Mom did, but have the advantage of some better ingredients and tools. I smash the olives with a mortar and pestle instead of a heavy glass.
I have good olive oil; she just used her vegetable oil. And I smash a few peppercorns to add in.
But Mom knew the olives weren't fantastic unless you let them marinate for at least a couple weeks. When I was a child, this was the only way I'd accept celery. Now I know it's just a spectacular seasoning for all kinds of things.
I have no recipe. It's a quart-sized deli container of large Sicilian olives, smashed open but not beaten up, a cup or so of chopped celery with leaves, half a dozen sliced garlic cloves, a few beaten black peppercorns, a couple tablespoons dried oregano, and olive oil drizzled over it until it's all just coated.
I keep it in the refrigerator until I can't bear waiting any longer. With olive oil, that means it will look semi-solid. But it can just be left out until warm. Mom sealed it in a jar and put it in the back of a cabinet. I was unlucky with that, though, so I did it only once.
People add things. Carrots, red pepper flakes, vinegar. I can't get with any of that. I guess you can put it in if you like, but to me, it's just in the way of the olives and celery.