Proof the yeast by adding the 1 1/2 tablespoon of active dry yeast, and 1 teaspoon of white sugar to 1 3/4 cup of warm water. It will bubble up and foam in about 5-10 minutes.
Meanwhile, in a mixer with a whisk attachment or bowl, add 1 1/2 cups of flour, the salt and the remaining sugar. When the yeast proofs, add it to the bowl with the oil. Then mix thoroughly.
Next, add another cup of flour with the 2 eggs. Mix with the whisk.
Add in the remaining flour one cup at a time. If using a mixer, switch to a dough hook.
Turn the dough out onto a floured surface and knead for 8-10 minutes (or until your arms give out). Move the dough into a buttered bowl and cover with plastic wrap. Place the bowl in a room temp area (an enclosed oven works!) for 2-6+ hours. The longer you let it rise, the fluffier the dough. You want it to double in size. You can punch it down midway if needed.
After the challah has risen (at least doubled in size), you'll divide it into 2 equal portions. Shape each portion into a rectangle, then roll out into a larger rectangle - approximately 10-11" wide by 12-16" high. Cut three strips in the rectangle. Each strip can then be filled with your filling choice, or simply rolled and left as-is.
Braid the strips. You will have 2 loaves. Preheat the oven to 350 degrees. Allow the braided loaves to rest for 30-60 minutes.
Brush the loaves with an egg wash, then place in the oven and bake for 24-30 minutes.