Freke,
I agree that you shouldn't have had to give that restaurant the recipes, but because I don't think that just because you work there, any intellectual property of yours or anyone else's who works there suddenly becomes the property of the restaurant (unless maybe you signed something to that effect?)
You cannot copyright the list or combination of the ingredients, or the techniques. The only thing that a copyright can apply to is the original way that the author writes and presents the recipe.
As a potential author of a book of your recipes, there is no problem for you to give out your recipes, as it is fine to compile and publish them again at a later date, since the recipe is not copyright-able anyway, just the way that you write it. And since the way you write something is almost always original (if you've ever studied linguistics,) there is no problem of you being the author. You should probably take into consideration who you give them to, as in how likely they are to share your secrets with others or credit you, things like that. And if you don't want to at all, that is not a bad idea, either. I wouldn't share any recipes that were very innovative/interesting.
About the areas of grey and that you don't buy that a recipe isn't special because it's just a list of ingredients and the differences between a home cook and a professional chef, I agree with you that it is all gray there, and rules concerning the dissemination of recipes among professionals are based on social norms, rather than anything legal.
However, there is no legal problem for the friend of the OP, who is home-baker selling cupcakes from a recipe from an article in the NYT. It would be considered polite manners to credit the developer of the recipe, and not represent it as her own, when asked for the recipe. However, since she is not in the same class as the professional chef of the original recipe (is neither a colleague or a rival,) it is ok if she doesn't advertise that it is not her recipe. Just like how the police don't raid Forever 21 for knocking off something designer (of course, if you're knocking off a designer logo, which is protected, that has problems.)
For example, if I wanted to perform a Mozart violin concerto and charge money for it, I am perfectly allowed to do so. I do have to obtain the music legally, and it is normal to tell the audience it is Mozart's K.433 or whatever.