This post pops up from time to time and everyone runs in to tell you to buy azugar rubio..but that is NOT brown sugar, that is simply unbleached sugar.
I have seen brown sugar from time to time at the Wong on Ovalo Gutierrez and the Vivanda and Pardo, but not on a regular basis.
I have, however, found molasses at several markets and mix a little of that with azucar rubio, you have the same thing.
http://www.joythebaker.com/blog/2010/08 ... own-sugar/
How to Make Brown Sugar
1 cup granulated cane sugar
1 Tablespoon unsulfured molasses
In a medium sized bowl, mix together the sugar and molasses. It’s that easy. There’s a part in this process where the molasses is super gunky and clumpy. You’ll think to yourself: Joy, you were wrong… this is coming out all wrong. Don’t worry. keep mixing it all together. It will even itself out. Work it until completely incorporated and no big molasses globs remain. For dark brown sugar, add another tablespoon of molasses. Use as you would in your favorite cake and cookie recipes. Store in an airtight container or in a ziplock bag with the air pressed out. Dang that’s easy!