Can I use brown sugar instead of white when making pecan pie? Or making anything else?
Yes you can. It's a 1:1 substitution. Brown sugar does bring a different flavor to a cake or pie than white sugar, so it may change the taste a little
I routinely do it, even when I have both on hand, when making pecan pie. I can attest that the flavor is much better. However, I caution a 1:1 substitution in certain other baked goods because brown sugar has a higher water content, which could affect other recipes where the moisture balance is more important. (Come back to the Hotline for other, more specific uses. I'm sure you'll get whatever help you need on those.) ;o)