(Update: I did make lasagna using the ricotta and mozzarella that I made, and it was delicious. :)
You need a thermometer that registers lower numbers like a dairy or meat thermometer. Most candy thermometers don't go that low. Also, use a non-reactive pot: stainless steel, glass, enamel. Here's an article on that. (click here)
1 gallon of whole milk
1 tsp citric acid
1/4 rennet tablet
1-2 tsp cheese salt
Remove it from the heat and mix in the rennet (diluted in 1/4 cup of water) for 20-30 seconds and then just let it sit for 20-30 minutes or until the curds are set. Some articles recommend letting it sit overnight to cure. I tried both. I think this is where raw unpasturized milk comes together much better but not so much the store-bought. My house is very cold in winter, so I don't know if this plays a factor or not.
When it thickens to a custard consistency, cut the curd into 1-inch (or so) squares. Gently reheat it to 105 degrees and then remove it from the heat again. Use a large spoon or ladle with slot to gently pull the curd out and strain in a strainer with cheesecloth in it. (Save the whey for other things.)
Let it sit and drain for a while and gently squeeze more of the whey out.
Put the curd in a microwave-safe bowl and heat for one minute on high and drain more whey out. You can use a wooden spoon to press it.
Cut the curd into 1-inch or so cubes and gently heat again, bringing the temperature up to 105 degrees.