Easy, relatively fast, and make the fluffiest brown sugar you could ask for. The whole process is actually really zen.
from Brownies for Dinner
1 Tbs. molasses (or 2 Tbs. for dark brown sugar)
1 cup granulated sugar
1. Pour sugar in a medium bowl, drizzle molasses over the sugar, trying not to touch the sides of the bowl, and use a fork to press molasses and sugar together to combine, until fully combined. Takes 5-10 minutes.