2-1/2 quarts popped popcorn 
1-1/2 cups light brown sugar 
3/4 cup dark corn syrup 
1/2 cup butter 
1 tablespoon vinegar 
1/2 teaspoon salt 
1 (6 ounce) package chocolate chips
1/2 cup chopped walnuts 
2 pints brick-style vanilla ice cream

Keep popcorn warm. In a 3-quart saucepan, combine brown sugar, corn syrup, butter, vinegar and salt. Cook and stir until sugar dissolves. Continue to cook until hard ball stage (250 degrees F on candy thermometer). Pour syrup over popped popcorn; stir to coat. Add chocolate chips and nuts; stir just to mix. Pour into two 13 x 9 x 2-inch pans, spreading and packing firmly. Cool. In each pan, cut 12 rectangles. Cut each pint of ice cream into 6 slices. Sandwich ice cream between two popcorn rectangles.
 

Source: http://www.nancys-kitchen.com