Place the sugar, yeast, and half the warm water in the bowl of an electric mixer (strong enough to handle five pounds of flour) Let the yeast proof for 15–20 minutes.

Add the flour, oil, eggs, and remaining water, alternating the wet and dry ingredients as you add. Add the kosher salt as a dough begins to form, and knead it on medium speed for seven to eight minutes.

Add the raisins and knead on low speed for one more minute, just until incorporated.

Place about one teaspoon of oil in the center of a large bowl. Transfer the dough into the bowl and flip it to coat completely with the oil. Cover the dough and let it rise for one hour.

Take challah, and discard the challah piece according to your minhag. Form the remaining dough into your desired shapes.

Combine the ingredients for egg wash and brush it on the dough. Let the dough rise for another 45 minutes to one hour. Meanwhile, preheat the oven to 375 degrees Fahrenheit.

(Optional:) Mix together the streusel ingredients with  your fingers until a crumbly consistency forms Sprinkle on top of the challah.

Bake large challos for 40 minutes, and smaller individual challos for about 25 minutes.