Slightly adapted from: Chow.com
Coat a large heatproof bowl with butter or oil and place popcorn in bowl. Toast pecans in oven at 350 F until fragrant, about 5 minutes.
Place sugar, corn syrup, water, vinegar, and salt in a medium saucepan and stir to combine. Place over high heat, stirring until sugar is dissolved, about 2 minutes. Bring to a boil and cook until mixture registers 260 F on a candy thermometer, about 5-7 minutes. Remove from heat and stir in butter, nutmeg, and vanilla until melted and smooth.
Immediately drizzle sugar mixture over popcorn. Add pecans and stir continuously with a rubber spatula, scraping the bottom of the bowl, until popcorn is thoroughly coated and cool enough to handle, about 3 minutes.
Using buttered or oiled hands, tightly press mixture (it may still be warm) into mini rounds. Place on waxed paper to cool completely, about 15 minutes.