From NJOP's Gourmet Shabbat:
Miriam Weinrib: CHALLAH (yields 5 medium challahs)
5 pounds flour
1 cup oil
3 tbsp. salt
4 ounces fresh yeast,
4 cups warm water
1½ cups sugar
1) Put flour, salt and sugar in a bowl, form a well in the flour.
2) Dissolve yeast into 2 cups of the warm water with 1 tbsp. sugar.
3) Pour into the well — let sit for five minutes until yeast bubbles.
4) Add oil, 4 eggs and the rest of the water.
5) Knead well until the dough becomes smooth and elastic. It should spring
back when pressed with the fingertips.
6) When dough rises (approx. 2 hrs.), separate an olive-sized piece, and thoroughly burn it. (If 5 or more lbs. of flour are used, recite the blessing--Ba’ruch Ah’tah Ah’doh’nai Eh’lo’hay’nu Melech ha’o’lam ah’sher kidishanu b’mitz’vo’tav v’tzee’vanu l’haph’reesh challah min ha’eesah Blessed are You, Lord our God, King of the universe, who has sanctified us in His commandments and commanded us to separate the challah from the dough--before burning).
7) Form loaves. Brush lightly with 1 egg beaten with 1 tsp. of sugar.
8) Bake at 350 F for 45-50 minutes until golden brown.