Attemped to make Fettuccine Alfredo for the first time. I used heavy cream, butter, shredded Romano and Parmigiano-Reggiano. I melted the butter over Med/Low, then slowly added the cheese a bit at a time. I brought the whole sauce to a slow simmer for a few minutes then took it off the fire. It tasted good. However, it was slightly gritty and I'm trying to figure out why. Did I bring the temp too high? Or maybe not high enough? How can I make it smooth?