In a small bowl, mix together the salt, garlic powder, and rosemary. If using butter for extra flavor, melt it in a microwave-safe bowl and set aside.

Place a heavy-bottomed 8-quart pan on the stovetop and heat over medium heat for 1 to 2 minutes or until pan is hot. You can check to make sure the pan is hot by dripping a drop or two of water into it - if it sizzles and evaporates, the pan is ready.

Add the olive oil and cover. Since the pan is already hot, the olive oil will heat quickly and begin to shimmer. You can drop a few kernels into the oil to test - when they pop, the oil is ready.

Add the remaining popcorn kernels and cover. Shake the pan just slightly to ensure that all of the kernels are covered in the oil. Return the pan to the heat and let it pop. You do not need to shake the pan. Just listen closely and when the corn stops popping, quickly remove the pan from the stovetop and remove the lid.

Pour the popcorn into a large bowl and alternate sprinkling with seasoning and melted butter (if using) and tossing the popcorn to evenly distribute the flavors. Serve immediately.