Heat the milk to 86-degrees. Turn off the heat. Add the mesophilic starter and mix thoroughly. Add one teaspoon of the diluted rennet and stir with an up-and-down motion.
Put the lid on the pot and let it sit for 12 hours.
Scoop the curds into a large cheesecloth lined colander.
Tie the ends of the cheesecloth and hang to drain for 12 hours.
In a large bowl, mix baking soda and salt into the cheese curds. BEAT WITH AN ELECTRIC MIXER. Yes, really.
Let sit for 30 minutes. The cheese will be light and airy after the baking soda is mixed in. Melt the butter in a large saucepan and add the cream (if using), stirring to combine. I use a big stir-fry (wok) pan.
Add the cheese and stir to combine with the butter and cream. Melt on low heat. Add cheese coloring, if you like, while the cheese is melting. If you choose to add coloring, add as much as you like until it looks how you want it to look. You can use the cheese white, if you prefer. I used about a dozen liquid cheese coloring drops to make it look like Velveeta. In about three minutes, you should have a beautiful, smooth cheese ready to go into whatever you want to use as a mold–or just scoop into plastic tubs. If you use a mold where you can take the cheese out easily, you can slice it.