I have a recipe for brownies that calls for baking it in a 9x12 AND an 8x8. I'd really rather bake it in one pan. What size pan would you use and how much would you increase the baking time?? Thanks!

9 x 12 = 108 sq in

8 x 8 = 64 sq in

108 + 64 = 172 sq in

Any pan that has an area of about 172 sq in would be fine - or  a bit smaller for a thicker brownie.

A 12 by 12 square would give a thicker brownie, a 14 by 14 would give thinner.

I'm not sure what other size rectangles people commonly use.

No idea about adjusting the cooking time. Test it after about the same amount of time and see if it's ready.

Thank you!