Preheat oven to 350°
Bottom layer: In a large mixing bowl combine: cake mix, 1 egg, melted margarine, and 2 tsp of pumpkin pie spice. Mix on low speed until crumbly.
Press mixture into bottom of a 15x10 pan (or 2 pie plates). Set aside.
Filling: In large mixing bowl, beat Cream Cheese until fluffy, gradually beat in Sweetened Condensed Milk, then remaining 2 Eggs, Pumpkin, and remaining 2 tsp. Pumpkin Pie Spice. Add Salt, mix well. Pour mixture over crust. (sprinkle with nuts,if desired)
Bake at 350 for 30-35 minutes, or until set.
Cool, chill. Cut into bars & store in refrigerator.
NOTE: If you don't have time to make this with the pound cake mix, the filling part also makes a great Pumpkin-Cheesecake Mousse, or you can pour filling part into an unbaked pie crust and then bake according to directions.