To make brown sugar soft again, place a slice of bread or a damp paper towel in the container with the brown sugar and seal it tightly. Leave it for a day or two to allow the moisture to soften the sugar.
No, it is not possible to make soft foam stiff again.
Cookie recipes moist and Soft not crunchy?
Find a recipe that looks good online. To make soft, chewy cookie
take the total amount of sugar (regular and brown) and make 80%
brown and 20% regular, use an egg or two in place of some of the
milk.
Where does brown come from?
Sugar in the raw is a pale amber color, that seems to be the
natural color.
Brown sugar is regular sugar with molasses added, thus the
reason it's soft and moist.