Challah (from Joy of Cooking)

A family holiday classic.

Ingredients

Combine 1/2 cup warm water (105ºF - 115ºF) and the active dry yeast in a large bowl or the bowl of a heavy-duty mixer and let stand until dissolved, about five minutes.
Add 1/2 cup bread flour, 2 eggs, 2 egg yolks, oil, sugar, and salt. Mix until thoroughly blended.
Gradually stir in the remaining 2.5 cups of bread flour
Knead for about 8 minutes until the dough is smooth and elastic and no longer sticks to your hands or the sides of your mixer's bowl.
Transfer the dough to an oiled bowl and turn it once to coat in oil. Cover with plastic wrap and let rise at warm room temperature until doubled, about 1 to 1.5 hours.
Punch down the dough and knead briefly, then return to the bowl and re-cover. Refrigerate until it has nearly doubled in volume, 2 to 12 hours.

Divide the dough into 3 pieces. On an unfloured work surface, roll into balls. Let the dough balls rest, loosely covered with plastic wrap, for 10 minutes.
Grease a baking sheet and sprinkle with cornmeal
Roll each dough ball into a 13-14in long rope, about 1.5 inches thick and slightly tapered at the ends, and dust lightly with flour.
Form the loaf by placing the three ropes side by side and pinching one end together. Braid the ropes together according to whichever method you prefer, and pinch together the other end. Tuck both ends under the loaf and set it on the prepared baking sheet.
Preheat the oven to 375ºF
Whisk together the last egg and a pinch of salt. Brush the loaf with the mixture and set aside the rest.
Loosely cover the braid with lightly oiled plastic wrap and set rise in a warm place until not quite doubled, about 45 minutes
Brush the loaf with the egg wash again. If desired, sprinkle with 1 Tbsp poppy or sesame seeds.
Bake until the crust is golden brown and the bottom of the loaf sounds hollow when tapped, 30-35 minutes. Let cool completely on a rack.