I make alfredo sauce from scratch. The recipe I use calls for 6tbsp. butter, 1cup cream or half and half, 1cup parmesan cheese. I hadn't made this in a while, but I have made it twice in the last month both times it broke. I did it he first time from memory and the last following the recipe with one exception I used a blend of four cheeses because I was out of parm. I don't know what I am doing wrong it was like thinned ricotta. I would love some ideas because all the times before it was perfect. I don't know what the difference is.
What works for me is about an extra 1/4 cup of parmesan and whisking in a little flour to thicken it up.
Ooops. I think I know what you did, since I also make fettucini alfredo from time to time.
1) you reduce the butter and cream
2) add hot, freshly cooked noodles
3) add cream and parmesan, toss
problem: if you are out of parmesan for step #3, you cannot randomly sub another type of cheese. The sub cheese has to be that dry, grated type: romano would be a good choice, and cheaper. Other, goopy, wet, melty type of cheese will not do. In this case, simply leave out the cheese in the last step. OK, not as tasty, but the recipe will work fine.
I make it all the time, melt butter, add 1/2 teaspoon flour (for me it helps to stabilize the sauce), just 1/2 teaspoon no more, then the cream and heat just a minute or two and add the parm or your favorite cheese, cook on low until melted.
One the cream could of been old, that is one cause, too high of heat, and to me is there is cheddar it tends to be more oily and tends to bread, but the flour always seems to fix that.
I make it 2x per month or more and only had 1 break probably 10 years ago.
I literally just throw it on a pot on the stove melt and let simmer, nothing more. It shouldn't be any harder.