Although I am not Italian, I have some information about Ricotta.
Ricotta in Italian means - RECOOKED. So, When you "cook"/make cheese, is the first time and the second time you "cook" the same substance (almost the same) you get the Ricotta.
The original Ricotta is made from whey only. About 10% whole milk may be added to get a greater yield. By adding cream you raise especially the fat content.
Making this stuff from milk only, is definitively NOT Ricotta, with a quite similar texture, but slightly different taste.
Ricotta may be coagulated with vinegar, lemon juice, yogurt. As a thumb rule, so called "Ricotta", may be made from 1 liter of milk adding 1 cup yogurt or 1-1/2 Tbs vinegar or 3 Tbs lemon juice. Heat the milk to 88-92 deg C, turn off the heat and add the coagulant, stir well and let the curds form.
I make my Ricotta as follows (minimum 4 liters whey):
Heat whey to 72-75 deg C (at this temp the rennet used for the cheese making, is killed and won't coagulate the added milk)
Add 10% Whole milk (might be unpasteurized raw milk) and stir
Heat the mixture to 88-90 deg C, turn off heat, give the liquid a thorough stir and drizzle in about 1/2 cup of vinegar moving from the center out. Curds should form instantly.
Let set for 5-15 minutes and transfer to draining moulds.
As Ricotta may be used in cooking sweet or salted, don't salt it now if you are not sure.
Tip: try making Gnocchi using Ricotta instead of potatoes.