Line a baking sheet with a clean kitchen towel or a few layers of paper towels; set aside. Cook cabbage leaves in a large pot of boiling salted water until bright green and pliable, about 2 minutes per batch. Transfer leaves to ice water, then to the baking sheet to drain.

Cook rice in the same pot until grains swell and rise to the surface, 3–6 minutes. Drain and rinse under cold running water.

Wipe out pot, pour in oil and cook onion until golden, about 7–9 minutes. Add pine nuts and cook until toasted. Mix in herbs, raisins, and sumac; cook until fragrant. Stir in lemon juice and let cool.

Combine onion mixture and egg with rice; season with salt and pepper. Prepare cabbage leaves by cutting out the thickest part of the rib. Place filling in the center and roll up.

Arrange rolls seam side down in the pot, add butter and water. Bring to a simmer, cover, and steam until cooked through, 18–25 minutes.

Serve cabbage rolls drizzled with oil, sprinkled with sumac and pepper, and with sour cream.