In a large bowl, combine one cup of granulated sugar with one tablespoon of molasses.
Use a spoon to mix the ingredients together until the molasses is evenly distributed throughout the sugar. I find it is much easier to just use your hands for this process.
Continue mixing until the mixture becomes uniform in color and texture.
Notes
For darker brown sugar, increase the amount of molasses used.
To store homemade brown sugar, transfer it to an airtight container and keep it at room temperature for up to six months.