a candy thermometer
2. Line a large shallow baking pan with foil, then lightly oil foil and a wooden spoon.
3. Melt butter in a 1- to 1 1/2-quart heavy saucepan over moderate heat. Add syrup and salt, then boil, without stirring, until mixture registers 300°F on thermometer, 15 to 20 minutes.
4. Pour syrup over pecans and popcorn, stirring briskly with oiled spoon to coat. Immediately spread popcorn in baking pan. Cool completely, then break into bite-size pieces.