What is the perfect ratio of brown sugar to granulated sugar in brownies?

Martha Stewart says that the amount and ratio of brown to white sugar actually doesn't make any difference in how fudgey the brownies turn out.

Faith Durand at the Kitchn, however, believes that adding dark brown sugar will make them chewier. I trust her on that. I'd go with half white and half dark brown sugar.

Durand makes this critical point however - one that's perfectly consistent with my experience:

Do not under any circumstances over bake the brownies if you want them to be chewy. In fact, err on the side of under baking them.

For more on this, see https://www.thekitchn.com/how-to-make-chewy-brownies-223699

;o)