When a recipe calls for brown sugar, could I use white sugar instead?
Yes!

Brown sugar is nothing more than white granular sugar plus molasses. That's it!

1 Tbsp molasses per cup of granular sugar = light brown sugar and 2 Tbsp molasses for dark brown sugar. There is no need to waste your money buying either, or worse, both.

Omitting the molasses and just using plain white sugar in a recipe will however change the taste somewhat in the finished product. You'll need to experiment to determine if that flavor change is acceptable to you and those you cook for.