As I have no eggs in the house, yet felt a need for brownies, I did some research and found that one small banana, mashed (1/4c) would be a suitable replacement for one egg. It was either that or unsweetened applesauce (no ground flaxseed on hand) and I figured the banana flavor would be OK with chocolate. It was Ghiradelli mix from the pantry, so not a big investment. I baked the brownies for the max recommended time and they were a bit underdone in the center to my taste. The banana taste is very faint, will see if DH notices...since I don’t plan to tell him.😏
Edit to add, the next day, no banana taste.