This recipe is milchig if you keep kosher. I've baked challahs with vegetable oil however the result is dramatically different in that it produces a much, much softer loaf. This recipe does not lend itself well to substitution with oil. Makes two large loaves.
3 packages active dry yeast
1 1/3 cups warm water (100 to 115 degrees)
1 tablespoon granulated sugar
1 tablespoon coarse salt
3 tablespoons softened unsalted butter
5 to 5 1/2 cups all purpose flour or bread flour( Gold Medal makes a decent bread flour).
1 egg yolk mixed with one tablespoon water
Poppy seeds and or sesame seeds (optional)
Combine yeast and water in a large bowl. Let stand for a few minutes until bubbles or foam are visible. Add sugar, salt, eggs, butter, and five cups of the flour, a cup at a time. Dough should be VERY stiff. If you have a stand mixer with a dough hook, use it to knead the dough for about five minutes until it is quite elastic and smooth. If kneading by hand, you have about ten minutes of hard labour ahead of you.
Place the dough in a large buttered bowl, turn once to coat, and cover tightly with plastic wrap and a kitchen towel. Place it somewhere warm and draft free for 1 1/2 to 2 hors or until doubled in bulk.
Punch the dough down and divide into six equal balls. Roll each ball into a rope and braid three together for each loaf. Pinch ends together well. Place the loaves on a buttered baking sheet. Cover again and let rise until almost doubled (about an hour).
Brush the tops of the loaves with egg wash and sprinkle with seeds (or coarse salt)if desired.
Bake in pre-heated 400 degree oven for 35-40 minutes. Check for hollow sounding bottoms. Cool on racks.