You will need (makes two challot):
1 kg, or approx. 6 cups, all-purpose flour
2 tbsp. fresh or dry yeast
4 tbsp. sugar
2 eggs, beaten
1/4 cup vegetable oil
1 tbsp. salt
about 1 1\2 cups water
To make your challah look even nicer:
1 egg, beaten
Mix flour, sugar and yeast in a large bowl (since our yeast were frozen, we first "revived" them with some warm water and a bit of sugar). Add eggs and oil, mix. Add salt. Gradually add water. Note: flour/water ratio may vary. The dough must be "kneadable", so you might find you need more/less flour or water. Knead until forming a smooth, elastic ball of dough. Oil your ball of dough slightly from all sides, cover with clean moist cloth and let rise for an hour and a half to two hours, until size doubles.
Knead dough again, until air comes out (you should feel and even hear it). Cover and leave to rise again, until dough doubles its size once more.
Pre-heat oven. In the original recipe, it says 200 C (or about 400 F), but we decided to be careful because our oven tends to burn baked goodies very quickly. So we went by 50 degrees lower, and it worked just fine for us. I think it's better to start with lower temperature and increase it later if you see the progress is very slow, than to start high and end up with challah that is burned on the outside and raw on the inside.
Divide the dough in half, and braid as desired. Place challot in baking tray, cover with cloth, and let rise for 30 minutes. Brush challot with beaten egg and sprinkle with sesame seeds. Pop into the oven and bake until golden.
Illustration photo: the Shabbat table
Note: we had little time left before Shabbat, so we were unable to let our challot rise for as long as the recipe suggested. The first two times, instead of an hour and a half to two hours, we only left our dough to rise for one hour each time. The last time, we skipped altogether. Still, it was beautiful, fluffy challah. We didn't even have time to braid it, and divided it into rather unimpressive buns (which is why there's no picture this time :o)). Anyway, it was really, really good.