1. In a small saucepan, melt margarine and brown sugar over a low heat. Slowly bring to a boil and allow to boil for one minute. Remove from heat and cool.
2. In a large mixing bowl, beat eggs and salt for 10 minutes. The mixture will become light in color and very fluffy. Slowly pour in the whipped topping and continue to beat an additional two minutes. (As you add in the whipped topping, the eggs may appear to lose volume and seem more runny, but they will firm up as the whip is incorporated.) Once the mixture forms stiff peaks, add the vanilla sugar and beat until combined. Then add the brown sugar mixture and beat until completely combined.
3. Divide the ice cream evenly between the two pie shells. Freeze until set (about three hours).
4. In a large bowl, beat the smaller container of whipped topping until stiff. Add confectioners’ sugar and vanilla extract.
5. Spread half of the whipped cream mixture over each ice cream pie.
6. Top with a sprinkling of crushed butterscotch candy, then cover and freeze.