The plain scones recipe ask for creme fraiche. Since it is a little pricey I did a bit of research and it turns out you can make it yourself with just heavy cream and buttermilk or yogurt. The best part? It is half the cost of buying it.
The key is to have pasteurized cream and buttermilk or yogurt. I read that the creme fraiche can be made with ultra-pasteurized dairy but it takes longer, 72 vs 12-24 hours. So where to get the pasteurized dairy in the city?
Whole Foods- Clover brand
The buttermilk or yogurt should ideally be full fat. I used 1% buttermilk. I have not found the full fat version.