Heat the olive oil in the heavy bottomed pot over medium-high heat and add the popcorn kernels. When the popcorns starts to pop, cover the pot tightly and continue to cook until all the popcorn pops, about 2 to 3 minutes, shaking the pot occasionally. Pour the popcorn into the large bowl.
While the popcorn pops, melt the butter in the sauté pan over medium-high heat until it is brown, shaking the pan occasionally. Remove the pan from the heat. Add the rosemary to the butter and let it sit for a minute or two to infuse the butter with flavor, then pour the butter mixture over the popcorn. Toss well. Add the salt and pepper and lemon zest and toss well.