This is so simple and quick to make that it is a crime to buy that stuff in a bottle. I'm giving you the basic recipe, and a bit lighter version as well. If you like this recipe, see more at my website: mybestcookbook.wordpress.com
Put the cream in a saucepan and warm slowly. As it warms, toss in the butter and allow to melt. When that is completed, add the cheese and stir until melted. You are done. You can add a bit of fresh grated nutmeg, or fresh herbs if you like.
A lighter version: Let the cream reduce to about 2/3 of a cup with a low simmer. Melt 1/2 stick of butter, and 2/3 c of Parmesan cheese.
If you noticed the general ratio is 1:1:1, but you can fudge this a bit, and obviously make the amount you wish, keeping the ratio in mind.