The quintessential cookbook?

UK, Any by Delia for beginners. When my son went to Uni I gave him her book. How to boil an egg.
Every recepie was for complete beginners.
He is now a great cook.

That kind of depends on how your cooking skills are right now.
Check out one called the "Good and Easy" cook book by Betty Crocker. I had an edition that was from the late 50's-early 60's that taught me sooo much about cooking. I also have a later edition that is pretty good too,just updated.

Try cooking magazines. I like taste of home. they have a huge selection of specializesd cooking magazines with real recipes you'd use every day.

Any of the Home and Garden or Betty Crocker books are okay for a newbie. The Joy of Cooking is also okay. But these are very basic cookbooks.
I would recommend a magazine called Cooks Illustrated. It is similar to a Consumer Reports on cooking. While they prepare a dish, they do it several different ways and explain what when wrong, how to correct it and make it better.

The Better Homes and Gardens cookbook, the red plaid one, is about $20 online. This book was given to new brides as a wedding gift and not only has 1500 recipes but teaches you how to cook. This was the go-to manual before the internet. But it isn't metric.

Go on line and search easy recipes, quick recipes, quick healthy recipes etc..... Find ones you like then print them out. Try them! If you like them put them in page protector sleeves then in a notebook where you’ll always have them at hand. You can also make notes on these recipes like add more oregano, omit the dill, try lemon juice instead of lime, cook 45 minutes instead of 35. As your collection grows you can make sure to keep the meats, veggies, desserts and whatnot separate. Also ask your mom, relatives and friends for recipes.
I’ve been doing this for years and my kids argue about who’s going to get my ‘cookbook’ one day.

An old classic, “The Joy of Cooking”.

I'd say the Joy of Cooking but I don't know if they have metric versions/conversions.

Your other option is Julia Child. Her stuff works .

In the UK? Delia, hands down. I know we make fun of her for being too pedantic sometimes, but you don't know what you don't know. She's the one to go to whenever you doubt yourself about any of the basics. Once you learn the basics it's easy to improvise or add your own twists. There are lots of fantastic websites out there for easy meal prep but sometimes you just want to read up on the basic basics and know that it's going to turn out and your ingredients won't be wasted.

After that the cookbooks I found most useful while I was a skint student were the cheap and cheerful cookbooks by Hermes House you used find in bargain bookshops at four for a fiver. Whoever the commissioning editor was they seemed to know what skint students had in their cupboards! I still use them too.

PS, if you spend money on only too things make sure to buy yourself a good quality general purpose chef's knife (like victornox) and a thick bottomed, medium saucepan with a lid (ikea 360 is value for money) as they will make everything easier.

Fannie Farmer - hands down the best cook book for beginners to experts. Really should be a teaching cook book you can find all kinds of good information about food products too. I will send you the 1.99 if you don't find it the best cookbook of all recommended.

Look for a 30-minute meal cook book.