Tangerines may not be the first fruit to come to mind when baking, but just like their fellow citrus fruits (think lemons, limes, and oranges, any of which could be substituted here), they make tart additions to a variety of sweets, including these muffins. The zest and juice are mixed into the otherwise basic batter that's given depth from brown sugar (rather than white sugar) and couldn't be easier to pull off.