I use Sour Cream in several recipes, is there a way to make it from scratch?
Sour cream is just cultured cream. You want to take fresh cream and then add the correct culture, then let it sit.
One way is to add a small amount of cultured buttermilk (with live cultures) to the cream. Put the mixture in a clean container and leave it in a warm place. In a day or two the cultures will have turned the cream "sour." and it's ready to use. At this point, you can use your fresh sour cream to start other sour creams as well.
Cultured buttermilk + cream = creme fraiche, not sour cream. The two are related, but sour cream has a much more pronounced sour tang. You need the right culture to make the real sour cream, I am not sure whether it's available for home purchase (but feel that it must be, with all the local farmers and artisan cheese makers). I grew up with real sour cream, made from only cream + added bacteria, and it's a very different animal from what's sold in stores in the U.S. To start with, its fat content is 30-40% (because it's really just heavy cream) and the consistency is much more liquid than store bought, sort of like homemade yogurt, but a little runnier. My mother's old recipes all call for "pouring" sour cream over dishes and adding starch if the dish needs to be thicker.