Mix together 2 1/2 cups flour with sugar, salt yeast (no need to dissolve first), water and oil. Mix in 4 eggs. Beat in 1 1/2 cups flour very well. Add 4-5 cups flour until a very soft dough is formed. Add raisins (optional). Knead for 10 to 15 minutes. Let rise 1-2 hours, or refrigerate overnight and then let warm to room temperature for 1-2 hours.

Make balls, roll them into ropes and braid. Let rise covered for 1/2 - 1 hour. Make an egg wash by beating the remaining egg. Brush on the challah. Bake in a preheated oven at 325 degrees F (150 degrees C) for 30 minutes. Apply the egg wash once more and bake another 30 minutes at 350 F (175 C). Makes 4 medium sized challahs.