Hope I'm not too late with this.
Angelina's is hell-and-gone from Chatelet, and though splendid (its
hot chocolate is the realllll treat, but gods, only after lunch) it
isn't my favourite Parisian tearoom, an honour belonging to the
incomparable Mariages frères in rue Bourg-Tibourg in the Marais, and
to Ladurée in Place Madeleine.
Neither is that great for breakfast, though. For that I suggest Café
Flore en Ile, on the Notre Dame end of the Ile St Louis. It is un
peu touristique, but the cafés are good, the croissants fine, and the
view incomparable.
If you want the BEST croissants, though, buy from someone great like
au Levain du Marais and carry it to a café, any café, and order a
café au lait, ands tuck in. Most caffs will shrug. Some will ask you to order.
Personally I tend to go out to a boulanger, take result back to hotel
room, eat it, do a musée, and have café at 11.
My other fave brunchy place is Le Stubli, but it's a metro trip from
you, in the 17th. Still, it's next door to a gggggrrrreat fromagerie.
NB _ I was in Paris last week, hence my silence on the
subject. Philippe Martin and Le Boulanger du Monge continue to do it
for me. Le plus bon pain du monde! But in case anyone is à Londres,
may I recommend St John Bread and Wine in Spitalfields, IMHO the best
bread in England? Which is not saying much, but is now saying
something. It's not as good as Acme, but better than many a loaf I
was served in SanFran.