In a large bowl, mix the yeast and sugar. Then dissolve them in warm water. Let stand for 5 min to proof it (make sure it bubbles).
Add the salt, oil and egg and mix thoroughly.
Gradually add flour 1 - 2 cups at a time, mixing after each addition. In my conditions, I add only up to 4.25 cups initially.
As mixture stiffens, begin kneading the dough until it becomes smooth and elastic. If it is still very sticky add more flour 1/4 cup at a time.
Knead for 15 minutes, add raisins if you want for the last 3 minutes of kneading.
Let rest in a large bowl for 45 min in a closed oven that has been warmed at 350 F for only 1 min (1st rise). Leave the oven light on (it helps maintain the temp).
Punch down the risen dough, split it in half, and then split each half into 3 parts.
Roll the 6 balls into sausage shapes, tapering the ends.
Braid into two loaves on a cookie sheet lined with parchment paper. To make an oval loaf, braid tightly at the start, loosely in the middle and tightly at the ends and tuck the ends of the braid underneath.
Place the tray back in the oven, and let rise for 1 hour with the light on. Remove risen loaves.
Preheat oven to 350 F.
Bake 25 minutes.
Remove loaves from oven, brush with a beaten whole egg and dust with sesame seeds. (If you are not using sesame seeds you can actually brush the egg on at the start of baking, but I have found that in my climate even the lightest touch of the brush can cause a bit of collapse, so you may want to do it this way regardless.)
Return to the 350 F oven for another 5 minutes.