Heat olive oil in a skillet over medium heat. Add chopped onions and sauté until translucent, about 5 minutes.

Add minced garlic and chicken livers to the skillet. Cook until the livers are browned on the outside but still slightly pink inside, about 10 minutes.

Remove from heat and let cool slightly.

Transfer the liver mixture to a food processor. Add butter, salt, and pepper. Pulse until smooth, adjusting seasoning if necessary.

Transfer to a serving bowl and refrigerate for at least 1 hour to allow flavors to meld.

Serve chilled on slices of rye bread, garnished with chopped parsley and pickles.