Set aside 2 tablespoons of the flour.

Place the remaining flour in the large bowl of an electric mixer fitted with a flat paddle or a dough hook.

Make a well in the center of the flour and pour in 1/4 cup of the warm water.

Sprinkle the yeast over the water and add 1 teaspoon of the sugar.

Using a fork, stir the water, yeast, and sugar together gently, keeping the mixture in the well.

Let stand until bubbly, about 10 minutes.

In a separate bowl, beat the eggs, the 1/4 cup oil, the remaining 1/4 cup sugar, and the salt together with a fork.

Add the egg mixture and the remaining 1/4 cup warm water to the flour mixture, and beat on low speed until incorporated.

Then beat on medium speed until smooth and silky, 5 to 10 minutes.

If the dough is too sticky, add the reserved 2 tablespoons flour (or more if necessary), 1 tablespoon at a time, and continue to mix for a few more minutes.

Oil a large bowl and place the ball of dough in it, turning the dough so it is oiled allover.

Cover with a kitchen towel and set aside in a warm place until the dough has almost doubled in bulk, at least 1 hour.

Punch the dough down and knead it by hand for 1 to 2 minutes, incorporating the raisins, if using.

For a braided challah, separate the dough into three equal portions and roll each portion out to form a strand 1 1/4 to 1 1/2 inches wide and about 12 inches long.

Braid the strands.

For a spiral Rosh Hashanah challah, roll the dough into a single rope about 34 inches long.

Wind the rope from the center of the spiral outward, keeping the center slightly elevated, like a turban.

Tuck the end under.

Lightly grease a baking sheet or line it with parchment paper.

Place the shaped dough on the prepared baking sheet, cover it with a slightly dampened cloth, and allow it to rise in a warm place for 1 hour.

Preheat the oven to 375 F.

Brush the top of the loaf with the egg wash, and sprinkle it with poppy seeds, if using.

Bake until the top is brown and the bottom sounds hollow when tapped with your fingers, 25 to 30 minutes.

Transfer the loaf to a wire rack and allow it to cool completely.