in a large pot, combine citric acid with 1/4 cup water and stir until dissolved.
Add milk, stir, heat to 90 degrees.
Stir rennet into water until dissolved.
When the milk and citric acid have reached 90 degrees (use an instant read thermometer) remove from heat, stir rennet (dissolved in 1/4 cup water also), stir until combined, and place a lid on it for 5 minutes. Do not touch or move or remove lid during this time.
After 5 minutes, check by putting your finger in and pulling back, this is what people refer to as a "clean break". You want to see the separation of the curds and the thin yellowy liquid (whey). If it does not look separated, let it go for another 5 minutes. Again, don't remove the lid during this final 5 minutes.
Once you get a "clean break", and the curds are nice and solid, cut a criss-cross-like pattern (or "checkerboard like pattern) through the pot, from left to right, and perpendicular to those lines, reaching the knife all the way to the bottom of the pan. Basically, you are just breaking the gelatinous whole into large chunks. Use a knife or offset spatula.
Return the pan to the burner, and heat to 105 degrees, only barely stirring to disperse heat, and not break up curds. Use an instant read thermometer to determine when the mixture has reached 105 degrees.
Using a large slotted spoon, or hand held strainer, transfer the curds to a fine mesh strainer or colander to drain.
Once the whey has drained off, pick up the remaining curds and squeeze a bit more over the bowl, further releasing some liquid, if possible.
Bring a large pot of water to almost boiling, but not actually bubbling. Once it looks like it's about to boil (about 180 degrees) remove from the heat. Lower the curds (they should be much tighter at this point) into the hot water. Note: The pot of water should be off the heat source now, this is done on the counter top. (See note for alternative microwaving technique below)
PUT ON YOUR HEAT SAFE GLOVES. Let the curds stay submerged in the hot water for a few minutes, while also reaching your hand in and squeezing them together to form them together. (Again, you can do this in the microwave if you want, but I prefer the hot water way...either way you have to wear the gloves! See recipe notes for microwave technique)
Remove them from the hot water, but keep the pot nearby. Fold and knead the curds together.
Stretch it out into a long strand, and fold it back up together into itself, kneading again.
Repeat this kneading and stretching for about 15 minutes. Submerge the cheese back into the hot water when it becomes tough and hard to stretch to soften it up and keep going. After about 15 minutes, the cheese should have a little sheen to it and seem very smooth and luscious. Tuck it into a little ball, pinching it neatly underneath itself.
Drop it into an ice bath for 5 minutes.
Done! Remove from the water and enjoy your cheese however way you like, or refrigerate for later use. Congratulations!
The more you do this, the more comfortable you will become with it. If the first go felt a little clumsy and confusing, just do it a time or two again and you'll feel much more confident. Always make sure you are not using ultra pasteurized milk, or your curds won't even form in the first place.