Using kitchen scissors or paring knife, cut each marshmallow into 4-6 pieces into a large mixing bowl (DO NOT use miniature marshmallows, it won't work; this step is sticky and a little tedious, but the results are so worth it!) Set aside.
In a mixing bowl, whip cream to stiff peak stage and set aside.
In a small saucepan, mix together well, egg yolks, sugar and vinegar.
Cook, stirring constantly, over medium/medium low heat until just thickened.
Remove from heat, add pineapple and stir until coated.
Pour mixture over marshmallows and mix very well (until all the marshmallow pieces are coated.)
Add whipped cream and fold in well.
Cover and refrigerate.
Before serving, give it an additional stir for final blending of flavors.