You can use oil instead of butter, the texture will be a little different, but they will be good! You can use an 8×8 pan. You could either try to cut the recipe down to 2/3 size, or put 1/3 of the batter in another baking dish, or you could put the full recipe in the 8×8 inch pan and have really thick brownies. The thicker brownies will require more baking time, say 35+ minutes, check for doneness by pushing a toothpick into the center and it’s done when it comes out clean. Enjoy!