ok so i looked up double cream and there is no american version of double cream. i would have to make it with buttermilk adn whipping cream. i think ill just try it with whipping cream. thats 36% fat rather than the 48%.
Double cream weighs in at 48% butterfat, or at least 8% higher than the highest-fat cream available in the United States — heavy cream or heavy whipping cream, which is 36% to 40% fat. British recipes call for double cream because they can — it's available and adds lots of richness to your dish. Will your cake flop if you use heavy cream? Almost certainly not.
Can you get a higher-fat cream to use in the recipe? Yes, with a little effort on your part. The first step is to prepare a homemade version of crème frâiche. Combine 2 tablespoons of buttermilk or sour cream with 2 cups of heavy cream. Heat the mixture to body temperature in a pan, and then let the mixture sit in a non-reactive container (stainless-steel, glass, or ceramic) in a warm place for 24 hours or so, until it thickens.
Step 2 is to line a strainer with a triple thickness of cheesecloth or a wet napkin, fill it with the crème frâiche, and suspend that over a container in the refrigerator. The whey will drain out of the cream, leaving it with a higher fat content. By the time about a quarter of a cup of whey drains from your 2 cups of crème frâiche, you will have a fat content around 48% to 50%.
http://www.ochef.com/843.htm