I don't live anywhere near Jeni's shops, so I've never bought her ice cream and cannot comment on whether these recipes really taste like what she sells at her shop. Other reviewers seem to say it does, so if you already love her ice cream, you might be very pleased with the book. I, on the other hand, found these recipes disappointing.
I got the book about a year ago, and have been experimenting with the recipes ever since. I was excited to learn of a technique for making egg free ice cream with a super smooth texture that will stay smooth even after freezer storage for days. Many ice cream recipes call for eggs, and cooking the egg/cream/milk/sugar mixture it into a custard. These custard based ice creams do stay nice and smooth in the freezer for a long time, but I was interested in learning about Jeni's egg free technique, for when I have no eggs or for when I'll be serving it to someone who cannot eat eggs.
All the recipes use an interesting strategy for binding the water, which helps prevent ice crystals from forming (ice crystals give ice cream a gritty texture). The milk/cream is boiled for 4 minutes to denature the proteins, then a corn starch slurry is added and it's cooked for another minute to thicken it. Some corn syrup is used because it is high in glucose, which binds water better than table sugar. Finally, cream cheese is added (or evaporated milk, in the case of one of the chocolate recipes), for "body".
I've made many batches with this technique, usually experimenting with either vanilla or chocolate, since we eat a lot of that, but I tried about 10 different flavors in all. Flavor and texture are good (I mean how can you go wrong with cream and sugar), but I have to say that there is not a single flavor using Jeni's technique that I prefer over the same flavor made with a custard base, or over uncooked ice cream. Every flavor tastes a little like cheese cake and cooked milk, and it melts into a paste in the warmth of my mouth, leaving a pasty after-feel. Some people I served it to found the thick texture to be sumptuously pleasant, but some of us (myself included) find it pasty and unpleasant. And I do like cheese cake, but do not want all of my ice cream flavors to taste like cheese cake.
I tried many different things to try to improve the flavor and reduce the pastiness, but nothing really resulted in an improved final product. In the end I decided that Jeni had pretty much optimized the technique, which, again, makes some pretty good, but not out of this world ice cream. And if I'm going to spend a lot of time and calories, and dirty so many dishes in the process, I want the result to be outrageously delicious.
Here is a summary of what I tried, FYI:
1. Substituted tapioca starch for corn starch (Jeni says she uses tapioca starch in her shop) - no difference.
2. Substituted tapioca syrup for corn syrup (jeni uses the former in her shop) - no difference.
3. Reduced amount of corn/tapioca starch - pastiness reduced, but texture less smooth.
4. Reduced cream cheese - tasted less like cheese cake, but then the unpleasant cooked flavor of the milk/cream is more prominent. So I came to the conclusion that the most important role of the cream cheese was to mask the cooked flavor, not to give the ice cream "body", and these recipes really do need the cream cheese to make the final product taste good. (Oh, just remembered: Jeni's suggestion of using organic valley cream cheese is right on. I tried Philadelphia, and it doesn't mix in as well into the ice cream base: the final product has annoying little tiny lumps of cream cheese throughout it.) I highly recommend warming the cream cheese before mixing it with the base, but the way, as this helps reduce clumping.
5. Reduced cooking time to 3 minutes: tastes better, but then final product not as smooth. I found it interesting that Jeni says milk proteins bind water better than egg proteins do. That's right, but only if you boil the bejesus out of the milk, making it taste funny. You have to cook it that much to denature the proteins so they will bind the water. Eggs, on the other hand, produce a delicious flavor and velvety texture just by cooking the mixture to 170 degrees to form a custard. That doesn't destroy the fresh flavor of the milk and cream, and the final product stays just as smooth after days of freezer storage.
So that's about it. It does dirty a lot of dishes: the saucepan for the milk/cream, a bowl for the corn starch slurry, and a bowl for the cream cheese. The 3 stars are for the beauty and engaging nature of the book, the novel technique, and the interesting flavor combinations. But the upshot is that I won't use Jeni's recipes very often, as it is a time consuming method that dirties lots of dishes, and the ice cream is just good, not great. Flavor and texture are just not quite right.
I would suggest trying out one of her recipes available online to see if you like this type of ice cream, before buying the book. Really it's a question of taste. Obviously the positive reviews say that a lot of people like this ice cream. Maybe it depends on what you are used to. And maybe Jeni's ice cream, with its corn syrup and pasty cornstarch base, approximates supermarket brands better than other home made ice creams do, which I wouldn't know, since I haven't had supermarket ice cream in many years.