Place the white sugar in a large bowl. Pour in the molasses and stir until well combined. You may need to get your fingers involved to break up bits of molasses and distribute it throughout the sugar.
Store in a nontransparent air-tight container. It will keep for months, however, it's recommended to add a brown sugar device or a slice of bread to prevent the brown sugar from clumping.
Notes
Nutritional estimate is provided for dark brown sugar.