1Coat a large heatproof bowl with butter, vegetable oil, or cooking spray and place the popcorn in the bowl.
2Place the sugar, corn syrup, water, vinegar, and salt in a medium saucepan and stir to combine. Place over high heat, stirring until the sugar has dissolved, about 2 minutes. Bring to a boil and cook until the mixture registers 260°F on a candy/fat thermometer, about 5 to 7 minutes. Remove from the heat and stir in the measured butter, nutmeg, and vanilla until melted and smooth.
3Immediately drizzle the sugar mixture over the popcorn. Add the pecans and stir continuously with a rubber spatula, scraping the bottom of the bowl, until the popcorn is thoroughly coated and cool enough to handle, about 3 minutes.
4Using buttered or oiled hands, tightly press the mixture (it may still be a bit warm) into 3-inch rounds. Place on waxed or parchment paper to cool completely, about 15 to 20 minutes.