The key to caramelized and very lightly charred popcorn is to keep shaking the pan as it cooks so the sugar doesn’t have a chance to burn before the kernels start to pop. Since the popcorn packet is sealed, it doesn’t absorb much smokey flavor, but you can add a gentle hint with a sprinkle of smoked salt after opening the foil.
disposable aluminum cake pan, heavy-duty foil and grilling tongs
Preheat a grill to medium high. (If using a charcoal grill, make sure that the coals are several inches below the grate.)
Combine the popcorn, vegetable oil, sugar and fine salt in an 8- to 9-inch round disposable aluminum cake pan and stir to coat. Tear off two 18-inch-long sheets of heavy-duty foil. Crimp the end of one sheet around the rim of the pan on one side, then crimp the other end of the foil on the opposite side of the pan, leaving 5 to 6 inches of room above the kernels so they have room to pop. Rotate the pan 90 degrees and repeat to crimp the second sheet of foil onto the pan, perpendicular to the first, making sure that the entire edge is well sealed. The foil should create a dome over the top of the pan.
Once the grill registers 350˚ F to 375˚ F, put the pan on the grill. Wait until you hear sizzling, about 2 minutes, then, using tongs, start shaking the pan frequently until the popcorn starts to pop, 3 to 5 minutes (it’s important to keep the pan moving so the sugar doesn’t burn before the kernels start to pop). Continue to cook, shaking almost constantly, until the popping subsides, 3 to 5 more minutes.
Remove the pan from the heat and let stand a few minutes. Carefully cut an X into the top of the foil and peel back the layers to expose the popcorn. Sprinkle with smoked sea salt. The popcorn will feel slightly sticky at first but will become crisp as it cools.
Popcorn needs room to pop: Form a dome over the pan using two crisscrossed sheets of foil; crimp against the edge of the pan.