Stir the popcorn kernels and 1/2 cup of the oil in a heavy large pot. Cover and cook over medium heat until the kernels have popped, shaking the pot halfway through cooking, about 3 minutes. Immediately transfer the popcorn to a large serving bowl. Toss the popcorn with the remaining 2 tablespoons oil. Sprinkle with salt, to taste, and serve.
Combine the oil and rosemary in a heavy small saucepan. Cook over medium-low heat for about 5 minutes. Remove from the heat and let cool to room temperature. Transfer the sprigs to a 4-ounce bottle or cruet. Add the oil and seal the lid. Refrigerate for up to 1 month.