In a small container, stir the yeast into 1/2 cup of warm water, then whisk in 1/4 cup of flour to make the sponge. Leave it in a warm place for 1 hour or until it has doubled in size.
When sponge is ready, in a large mixing bowl whisk together the remaining flour & the salt, then make a well in the center.
Into the well, add the sponge, along with 3-4 tablespoons water, the oil & sugar, gradually incorporating the flour into the other ingredients.
Knead for 10-15 minutes or until the dough is smooth & elastic, then leave it in a warm place for about 1 hour, or until doubled in size.
When ready, punch the dough down & divide it into 8 pieces. Lightly flour a working surface AND hands & roll each piece into a sausage shape, then let rest 10-15 minutes.
After that, roll the dough into a longer sausage shape ~ You will probably have to let the rolls rest once more in order to stretch them to the length they need to be, 20-25 inches long.
During the 15 minutes that the dough is resting for the last time, line a large baking sheet with parchment paper, then spread the sesame seeds in a large baking dish & have the egg whites ready in a wide, shallow bowl.
Dip the long rolls into the egg white & then roll them in the sesame seeds. Twist 2 of them together & join the ends to form a ring about 4-5 inches in diameter. Shape the remaining rolls in the same way, then let them rise for about half an hour.
About half way through this rising, preheat the oven to 400 degrees F.
When ready, bake the galettes for 15-20 minutes or until golden & slightly crisp on the outside. Let cool on a wire rack & serve at room temperature the same day OR freeze for later use. Simply reheat before serving any that have been frozen & then defrosted.