Gloria (Peck) Schwartz's Challah

1 yeast cake
2 tsp. sugar
1¼ c. warm water
4½ c. sifted flour
2 tsp. salad oil
1 tsp. salt
2 eggs
1 egg yolk
raisins -- optional

Combine yeast, sugar, and ¼ c. warm water and let stand 5 minutes. Sift flour and salt into bowl, making a well in center. Drop in eggs, oil, remaining water, and yeast mixture. Work into flour. Knead in a floured surface until smooth and elastic. Place in bowl and brush top with a little oil. Cover with a towel and set in a warm place for one hour. (it will rise.) You can place it in the oven with a pot of steaming water under the rack. Close oven door. 

After one hour, punch down and cover again. Let stand until double in bulk. (Another hour.) Divide dough into three equal parts. Flour hands and roll dough into three equal lengths. At this time, add raisins, if desired, pushing them into the strips. Braid strips and place on baking pan. (Be sure no raisins are exposed or they will burn.) Cover and let stand until double in bulk (about one hour). Brush with egg yolk. Bake about 50 minutes in a 350 degree oven.