Use a wide, shallow bowl or plate rather than a deep bowl so every dip gets a bit of everything rather than just oil.
Castelvetrano olives are mild, buttery, and slightly sweet which makes them the right choice here. Kalamata olives can substitute for a more assertive, brinier flavor.
Freshly grated Parmesan from a block dissolves into the oil much more beautifully than pre-grated. Use a Microplane for the finest, most evenly distributed result.
Warm the bread before serving. Warm, slightly crusty bread against the room temperature dip is the best possible version of this appetizer.