In a large, heavy-bottomed saucepan over medium heat, add the duck fat and four corn kernels over medium heat. Cover the pot and wait for the "test" kernels to pop.
When all four kernels have popped, add the remaining popping corn and a pinch of salt to the pan. Cover and gently shake the pan to distribute the kernels.
Once the kernels start popping, tip the lid just a touch to allow steam to escape. Continue to gently shake the pan over medium heat until popping sounds are spaced a few seconds apart.
Remove from heat and take off the lid. Pour into your serving bowl. Sprinkle remaining salt onto popped corn and stir.
Transfer the warm popcorn to a large bowl and add the butter and truffle salt. Toss well to coat the popcorn. Add the parmesan, rosemary, salt, and pepper. Toss well.
Spicy Buffalo Wing
In a small bowl, mix together the paprika, cayenne, and salt. In a separate small bowl, mix together the sugar, wing sauce, and melted butter. Pour the wing sauce mixture over the popcorn. Carefully toss to coat. Sprinkle the dry spice mixture over the popcorn and stir to coat evenly.