Sauté over low heat the olive oil, onions, garlic and herbs. Add rice and water. Bring to medium heat, stirring occasionally, until all water is absorbed. Remove from heat; add lemon juice and pepper. Set aside. Boil grape leaves 10 minutes, until tender. Drain leaves; stuff with rice mixture; the shiny sides of the leaves face out. Cover the bottom of an 8-quart saucepan with single leaves; place stuffed leaves on top; cover with more single leaves. Cover with water; add butter. Place a dinner plate over the leaves (to keep them firm) while simmering over low heat for 1 hour. Drain; chill 1 hour before serving plain, or with yogurt for dipping.