First, pour the whole gallon of whole milk into a very large bowl. Microwave the milk for 55 minutes and 55 seconds. Halfway through, use a fork to remove any skin that has developed on top and discard. Continue to microwave until finished. Carefully remove the bowl from the microwave and place it on the counter.
Allow the milk to cool to room temperature. As it cools, it will likely develop another skin on top. Again, remove and discard the skin.
After the milk finally cools, after a few hours, gently mix in the store-bought or homemade leban. Cover the bowl with aluminum foil and then cover it with a blanket or thick towel. Allow this mixture to sit out at room temperature overnight.
The next day, during the morning or afternoon, remove the blanket and foil. Place about three or four layers of paper towels gently on top of the surface of the leban. Re-cover with the foil and place it in the fridge to cool overnight. The next day or whenever you're ready to serve it, gently peel of a portion of the paper towels. Scoop out as much leban as you need and enjoy.
Be sure that after you use what you need, place the paper towels back onto the top and cover it back up with the foil. Then, store it in the fridge until you're ready to use more. Leban lasts up to two weeks in the fridge. Enjoy!