Hi Marggie, found this on the Internet, hope it helps.
In a recent live chat, Delia explained, ‘Fromage frais is a dairy product with either 2 per cent fat or 8 per cent fat. So really it’s a low-fat alternative to cream.
Fromage frais is a term used to describe very young fresh cheese and the best substitute is quark. You could also blend equal parts of cottage cheese and yoghurt until smooth, or use Greek-style yoghurt. Do not heat these too much, though, or they will curdle.
Crème fraiche can be substituted by mixing equal quantities of liqhtly whipped double cream with Greek yoghurt (or another thick yoghurt), but if it’s being heated you have to be careful not to let it boil. Alternatively, add a drop or two of lemon juice to some lightly whipped cream, or mix equal quantities of lightly whipped cream with soured cream, then leave at room temperature for about eight hours before refrigerating.