Make Your Own Creme Fraiche

I made my own creme fraiche yesterday after reading a very inspiring issue of Sunset Magazine. The recipe called for 1 cup of heavy whipping cream and 2 tablespoons of buttermilk. You mix it up and then let it sit until it thickens, which the recipe suggested could take 8 hours or overnight. I found it took over 24 hours to get it to the right consistency. This might be because I used pasteurized whipping cream. It might also be due to the fact that I did not cook the cream to 105 degrees like other websites suggested. Eh. It still works. The result was creme fraichey, but a little runny. I think that I will leave it out for maybe 32 hours next time to get a real firm consistency. I have never had the luxury of having too much creme fraiche, so I think I will make Ina Garten's Mustard Roasted Fish which calls for 8 oz of creme fraiche.