I like A Year in a Vegetarian Kitchen by Jack Bishop. The recipes are fairly simple, take advantage of some prepared ingredients and are arranged seasonally. My daughter is vegetarian so I’ve tried out a number of vegetarian cookbooks over the years and liked this one a lot.
Sorry @Iglooo , I didn’t realize you were the OP!
Yes, I make notes on my Pinterest recipes, my NYTimes recipe box, etc. 
Yes I agree that Ottolenghi recipes are sometimes time consuming. But not all of them! And they are simplifiable. For example I make the eggplant dish on the cover all the time. I usually grill the eggplant. I don’t even measure the yogurt/buttermilk sauce any more. If I’m out of buttermilk I don’t worry about it. If I can’t find pomegranates I’ve left them out or made substitutions.
Look at Marian Morash’s The Victory Garden Cookbook. Morash often appeared on the early days of the PBS tv show Victory Garden–her husband was the producer. The book has multiple recipes for almost every vegetable. Some are quick and easy, others are more time consuming. For all the vegetables, she provides multiple prep methods (grill, braise, etc.). Plus, she explains how to preserve the vegetables. You can find used copies of the book on Amazon.
https://www.amazon.com/Victory-Garden-Cookbook-Marian-Morash/dp/039470780X
My youngest D is a vegetarian and I gave her a copy of this book–she loves it.
I have given my son and several young adult relatives the Better Homes and Gardens new Cookbook- my last edition is the 14th one. It is not a vegetarian cookbook but is a great reference for how to do everything basic. Cooking vegetables, pictures of types of pasta and cheeses for example. Later editions are more in tune with modern eating than those from decades ago. She can skip the cuts of meats pages like I do. A nice reference to have on the shelf to aid in learning cooking basics. You can get so much online but it is nice to just open a book and find out what various greens look like and how to cook various beans (I just looked- there’s a chart).
This cookbook is complete in covering so many different cooking techniques and foods. You then supplement it with books of recipes. Good for how to cook, not just needing to follow a recipe.