1 gallon / 4 liters of full fat milk 1 cup of buttermilk* Additionally: Cheese cloth
Disinfect a glass or ceramic container big enough to fit 1 gallon of milk + 1 cup of buttermilk by pouring hot water into it. Pour milk and buttermilk into in and set on the counter for 72 hours (or more). When milk becomes solid (and is no longer "slimy") to where you can slice it and it will stay separated, it is ready. Consistency should resemble sour cream or Greek yoghurt.
Pour into a large boiling pot, cover and heat on the lowest heat setting until whey separates from curds and the curds start hardening. Don't stir. I "cooked" mine for about 1 hour. Curds should be a bit hard, kind of like cottage cheese. If still mushy, keep heating.
When "cooked" place cheese cloth over a strainer and pour liquid through. Let sit for about 10 min to drain. To get rid of extra liquid, twist cheese cloth to squeeze it out. Leave some moisture though, you don't want it too dry.
When satisfied with the moisture level, transfer into a container and refrigerate.
* If using unpasteurized milk, skip adding buttermilk.