In the stainless steel pot you made the Mozzarella add a quart of milk or half & half to the whey. Heat to 200 degrees using a thermometer to measure the temperature. You will need to stir every minute or two so that you don't boil it or it will taste burned.
Once the temperature gets to 200 degrees which will take about 15 - 20 minutes you will stir in the cider vinegar and then remove the pot from the heat. Let sit for 5 minutes for the vinegar to activate or acidify the whey.
In a cheesecloth lined colander pour the whey into the cloth and let the remaining whey drain out of the cloth into the sink or a bowl. It will take about 20 minutes to completely drain and what you will have left is the beautiful Ricotta.
Scoop the Ricotta into a recycled yogurt pint or Ball jar and put into the fridge. The cheese will last about 2 to 3 weeks.