In a large pot, add the oil, swirling the pot so that the oil entirely coats the bottom. Add in truffle oil and rosemary. Top with kernels, spreading them in a single layer over the bottom of the pot.

Pop popcorn over medium-high heat. When popcorn is ready, drizzle with an additional capful of truffle oil and sprinkle with popcorn salt. You can prepare this popcorn a day ahead and store in an airtight container.