Prepare two eight by four inch (20×10-centimeter) loaf pans. Cut two pieces of aluminum foil, one for the length and one for the width of the pan. Make each piece long enough to extend over the rim of the pan. Press the pieces of foil into the pan as neatly as possible, gently pressing into the corners. Fold the excess foil over the rim. Spray the bottom and sides of the pan with cooking spray. Set the pans aside.

For the praline layer, microwave the praline paste in 20-second increments until soft and easy to work with.

In a large mixing bowl, cream the margarine. Add the vanilla. Add four tablespoons sugar and beat on medium speed for three minutes. Add one egg yolk at a time, scraping the bowl between each addition. After adding the last yolk, beat four minutes until very creamy. Add in softened praline paste and beat just until blended. Transfer to a medium mixing bowl.

In a clean and dry mixing bowl, beat egg whites and salt. Slowly add in the remaining two tablespoons sugar. Beat to soft peaks (do not overbeat). Slowly fold the whites into the praline mixture.

Divide the praline mixture evenly between the two loaf pans. Freeze for at least one hour.

For the chocolate layer, melt the praline paste and chocolate in a double boiler or microwave in 20-second increments. Stir until melted and combined.

Repeat the steps for making the praline mixture, replacing the praline mixture with the chocolate mixture. (Use all except two tablespoons sugar in the first step; reserve the two tablespoons sugar for beating with the egg whites.) Divide the chocolate mixture evenly between the two loaf pans. Place a piece of plastic wrap over the chocolate layer and smooth. Freeze for six hours.

Place a serving plate in the freezer for 10 minutes. Remove the truffle from the freezer. Remove the plastic wrap and loosen the foil from the pan edges. Place the chilled plate over the top and invert the frozen truffle onto the chilled plate. Remove pan and peel off the foil.

The plate may be returned to the freezer until ready to serve. Even out the edges and slice down the entire length, then slice widthwise into eight so you have 16 portions.