In a mixer bowl, add leaven, seltzer, sugar, oil, eggs, and most of the flour (reserve a few hundred grams, about 1 cup). Knead for about two to four minutes. Let sit for about 15 minutes.

Add salt and remaining flour; knead for about five to eight minutes. If the edges are sticking a lot to the edge of the bowl, add 100–200 grams of additional flour. It’s normal for the dough to be somewhat sticky.

Spray a large container with cooking spray. Place dough in container and cover. Let rise for two hours. (Optional: lift, stretch and fold over the edges twice during that time.) Then refrigerate for six to 12 hours. Remove from fridge.

Heat oven to 175 degrees Fahrenheit. When preheated, turn off the oven. Place dough into challah pans about halfway full (te dough will be too sticky to braid). Cover pans and place in warm oven for one-and-a-half to two hours.

Remove challahs from oven and egg wash them while oven is preheating to 400 degrees Fahrenheit. (I like to sprinkle everything spice or press a few chocolate chips into the challah).

Bake for 10 minutes. Lower to 350 degrees Fahrenheit and bake for about 30 minutes or until golden brown.