There's a tiny stall near the international San Juan Market (metro: Salto de Agua) that I like to visit every time I'm in that neck of the woods. It's called Molinera El Progreso, a culinary delight stacked floor to ceiling with herbs, spices, sugars, flours, and nuts--either whole or powdered. After checking everything off the list at the market for your special dinner of exotic meats, it makes perfect sense to stop off at the next block and pick up the exotic herbs and spices you're going to need for that one and only time you'll ever need them. Stand back, move your eyes up and down, left to right, and be awed by the number of items en polvo! Grab as little or as much as you need, and if they don't have something you're looking for, say mango powder (for mango pudding, of course), they'd gladly do it for you.
Address: Molinera El Progreso Calle Aranda 26 Colonia Centro México D.F. (55) 5512 2844 Click here for a map.