Preheat oven to 250 degrees. Combine popcorn and nuts in a large 4-inch deep, buttered baking pan. Keep warm in the oven.
Butter two 8x8 inch baking pans. Mix together molasses, sugar, butter, vinegar and water. Cook slowly, without stirring, until mixture reaches 250 degrees on a candy thermometer.
Add baking soda and mix well. Remove from heat and quickly stir in vanilla.
Remove popcorn and nuts from oven. Pour mixture over and mix well. Pour into buttered 8x8 pans. Cut when cool. Makes 24 squares.