Dissolve yeast and sugar in water, and add 1 cup water to make a slurry. Let stand briefly or up to an hour. Add salt, oil and 2 eggs. Gradually add flour until dough is firm but not overly sticky. Knead for 5-10 minutes by hand (or 3 minutes if using a standing mixer with dough hook) until firm and smooth. It should bounce back when poked. Place dough in oiled bowl and cover. Let rise 1½-3 hours at room temperature or a full day or overnight in the refrigerator. If you refrigerate, let the dough come to room temperature before continuing.
Preheat oven to 350°. Put dough on board lightly dusted with flour. Divide into portions for braiding. You can add raisins or cranberries at this point—work into dough before braiding. After braiding, let rise anywhere from 10-40 minutes at room temperature. Brush with one egg yolk mixed with a small amount of water. A few minutes later, repeat wash for extra shine. Sprinkle with seeds if desired. Bake 20-25 minutes until golden.