Place popcorn in a large bowl. In a small microwave-safe bowl, melt butter; whisk in the pudding mix, corn syrup, vanilla and salt until smooth.
Microwave, uncovered, for 45 seconds or until bubbly. Pour over popcorn; toss to coat. Spread in a 15-in. x 10-in. x 1-in. baking pan coated with cooking spray.
Bake at 250° for 25-30 minutes or until crisp, stirring once. Remove popcorn from pan to waxed paper to cool. Break into clusters. Store in airtight containers. Yield: 12 cups.