My uncle has two pastry chefs at this famous resturant in Little Italy, NYC. I called and you must purchase the cheese. There is nothing you can add. The cheese comes in two varieties.
One is 4% fromage frais which is lower in fat. The other is 8% fromage frais. The cream is added when the cheese is being made at the dairy. Adding of the cream occurs only during the cheese making process. It is the same concept as cottage cheese, it comes in 1%, 2%, etc.
That is why I gave you ino related to what fromage frais is.
I teach cooking as a hobby at a local high school at night.
If you tell me precisely what you are going to be preparing I can help you. Adding cream to your recipe may not be a good idea.
Refer back to this from Delia, she is explaining how the cheese is made:
Fromage frais is a fresh curd cheese introduced to this country from France and made from pasteurised cows’ milk. Basically, it has very little fat, but cream is added to make 4 per cent (or 8 per cent) fromage frais. The 4 per cent is fine eaten on its own with honey or fruit purée, or used as a topping – especially for anyone on a low-fat diet. The 8 per cent is the best one for cooking. Either of these can be used in savoury sauces or as a topping for jacket potatoes with a few snipped chives. Alternatively, there is a diet, virtually fat-free version (0.1 per cent), which is ideal in dips. For a cool, light, low-fat dessert, see the recipe for individual fromage frais puddings with red fruit compote.