Located in Roma Norte, Panadería Rosetta makes some of the most incredible baked goods that I have ever had the luxury of tasting. The coffee and espresso drinks here are also note-worthy, using beans sourced exclusively from small Mexican producers. This location is tiny and there is often a line, so be prepared to take your food to-go. Luckily it is right around the corner from Plaza Rio de Janeiro, a lovely little park with benches and a large, central fountain that features a giant replica of Michaelangelo’s David. I prefer sitting on the benches that have a view of his sweet, sweet buns but the choice is yours. If you're more mature than I am and want to gaze elsewhere, it is also great for people/dog watching while enjoying a coffee and a delicious meal before exploring more of the city. Some of my favorite menu items include the rollos de romero (both sweet & savory, these tiny rosemary rolls top any cinnamon roll I've had, I think they use some kind of pork fat in the recipe), the focaccia (the best I've ever had), and the ham & cheese croissant. When visiting Mexico City, I usually make it a point to rent an apartment within walking distance of this place and start my day there almost every morning.
More info here: http://www.rosetta.com.mx/panaderia-en/panaderia.html