Dissolve the acid in 1/4 cup water. When the milk is at 90°F pour in the citric acid. Let it sit for 10 minutes.
Stir in the rennet and milk A solution into milk B. Stir for two minutes.
Put the lid on and let it set for 30 minutes. You're trying to achieve a "clean break" which is when the milk sets. Wait longer if need be (some people wait 3 hours).
Line a colander with a cheesecloth. Pour the curds and whey into the cheesecloth and let it drain.
Gather the ends of the cheesecloth and massage the bag to drain the whey until it resembles a solid mass of curds.
Microwave for 1 minute. Drain the whey
Microwave in 20-30 second increments 2-3 times until the cheese is no longer releasing whey. You want to get a reading of 135°F.
It's time to knead the cheese a bit until you get the stretch texture of mozzarella. I recommend using gloves as it gets really hot. Add salt and knead a bit.
Shape and drop it into some cold water to "set" it.