Here is a full proof Challah recipe.

Source: Jennie Grossinger's "The Art of Jewish Cooking"

Yield: 1 very large or 2 large challahs

Prep time is 3 hours of rising
Cooking time is about 40-50 minutes

1 package yeast
2 teaspoons sugar
1/4 cup lukewarm water
1 cup lukewarm water
4-1/2 cups sifted flour (you can sift a little extra and set it aside to have to work with)
2 teaspoons salt
2 eggs
2 tablespoons salad oil
1 egg yolk (possibly 2)
4 tablespoons poppy seeds (optional)

Combine the yeast, sugar and 1/4 cup lukewarm water. Let stand 5 minutes to proof (until the liquid-yeast mixture gets a nice layer of foam on top)

Sift the flour and salt into a bowl.

Make a well in the center and drop the eggs, oil, 1 cup lukewarm water, and the yeast mixture into it. Work into the flour. Knead on a floured surface until smooth and elastic.

Optional method to hand kneading: Place the ingredients into KitchenAid bowl, attach the dough hook and let it go until the dough has a spongy texture.

Place in a bowl and brush the top with a little oil. Cover with a towel, set in a warm place, cover and let rise 1 hour. Punch down, cover again and let rise until double in bulk, (one more hour).

Divide the dough into three equal parts. Between lightly floured hands roll the dough into three strips of even length. On a cookie sheet lined with aluminum foil (you can dust it with cornmeal if you like) braid them together. Cover with a towel and let rise until double in bulk (one hour).

Preheat oven to 375°F

The egg yolk is to paint the challah. Brush the braided challah and if you made one large one, you may need two egg yolks and then sprinkle with the poppy seeds (optional).

Bake in a 375°F oven 50 minutes or until browned. To see if it is done, turn it over and thump it, it should sound hallow.

Makes 1 very large challah. If you wish, divide the dough into 6 parts and make two large loaves, or make one loaf and many small rolls.

Let it rest for a few minutes before slicing.

Make certain you wrap up any uneaten challah as it will go bad as there are no preservatives in it.

L'shanah tovah tikatev v'taihatem