How we met: Charlotte Mendelson and Baroness Julia Neuberger

The novelist Charlotte Mendelson was born in 1972 and grew up in Oxford. She published her first book, Love in Idleness, aged 29. The second, Daughters of Jerusalem, won the Somerset Maugham Award. The protagonist of her third novel, When We Were Bad, published this month, is a female rabbi. She lives in north London with her partner and their two children.

I am Jewish but was brought up not practising at all. I was confused about how one could be Jewish and yet not know anything about it. Julia was the first person I'd met who was an example of how to be Jewish without either being enormously observant or without thinking about it at all. She was relaxed but knowledgeable, and liberal in every sense.

I was 22 and had just started in publishing when Julia's editor asked if I wanted to work on her book about being Jewish. All I knew about her was that she was a woman rabbi, and like most non-practising people I thought rabbis were men with big beards, which of course she isn't. When her book came out she gave me an incredibly nice acknowledgement and invited me to a dinner at the Groucho. I couldn't believe it and I felt very privileged. I can't remember exactly how the bonding took place, but during the course of the evening Julia offered to be my godmother and I said yes, a bit astonished by my luck.

I was new in London and didn't know many people and Julia would have me over for Friday nights. She is a fantastic cook and her family are all lovely, but it also gave me a bit of spiritual sustenance that I hadn't expected I wanted.

Julia is an amazing, warm, very capable and giving person. When I had kids I started wanting to do a little more and Julia had to come round and give me a crash course in how to do Friday nights.

When I started thinking about my third novel, five years ago, I wanted to write about what it feels like to be a liberal Jew in England. I wanted the mother of the family to be charismatic and dominant and quite well-known, so it made sense for her to be a woman rabbi. The character, Claudia, is not at all based on Julia, but I interviewed her and she gave me fantastic introductions to other women rabbis.

So many people love Julia and I wouldn't assume that I'm particularly important to her, but she's important to me. I'd like to give her something back but I'm aware that, in a way, I can't. Writing this book, I worried other Jews might hate me for putting my head above the parapet, but Julia said perhaps I could be a crusader for Jews like me who don't have a community. That would be amazing.

Apart from that they're both sociable and hospitable and fun, Julia is nothing like my mother and in no way a substitute, but I'm very proud of being her god daughter. I can't imagine being more on the same wavelength with another rabbi.

Baroness Julia Neuberger, 57, is a rabbi and Liberal Democrat whip in the House of Lords. She was the UK's second female rabbi and the first to have her own synagogue. She was chief executive of the health charity The King's Fund, and her books include The Moral State We're In. Her husband, Professor Anthony Neuberger, works at Warwick Business School and they have two children. She divides her time between north London and Warwick.

Charlotte's not someone who stands on the sidelines much; she really wants to get involved. Long before she had any experience of editing, my editor let her do some work on my book and she would say to me, "I think it would be better if you took this bit out." She was so enthusiastic, like a ball of fire. She was really very young, and very pretty, but the most inspirational thing about her was that she just didn't have any world-weariness about her at all.

I think she was interested in working on my book because it was about being Jewish and she was trying to work out what to do about her Jewishness. Back then, 12 or 13 years ago when she was very young and I was relatively well known, she was very good at just sitting opposite me and asking me what I meant, so she could clarify what I was saying.

We got talking about her ambivalence about being Jewish and she wanted to know more about what it meant for her. She appointed herself my honorary god daughter and she used to come round for supper on Friday nights. She was always thirsty for knowledge. When she had the children she wanted to learn how to do it herself and would ring up and say, "Have I got this right? Is it OK if I do it like that?"

One of the reasons we get on so well is that we both read voraciously, but I'm not a writer like Charlotte is. I write to get my ideas across and am more naturally a talker. She is a terrific writer and a very good editor. She would send me passages of her latest book and we had lots of conversations around the theme. She would consistently check things with me about it, more the flavour of it than specific facts. She's very young but I can see that her writing is getting deeper and better and she's exploring some quite complicated themes. I think this novel is very good, but I hope it's not about me!

Sometimes we see each other a lot and sometimes we don't, but we can always pick the phone. I had an operation some months ago and she came to see me and she brought her son Theodore to Passover. She's very welcome to any Jewish things we do but she has to find her own way and make her own choices. I give her advice but I never push her. Had her parents forced Judaism down her throat, she might have been very negative about it - parents can never win. s

'When We Were Bad' by Charlotte Mendelson is published by Picador on May 4, priced £12.99