Combine marshmallows and milk in a saucepan on low heat. Cook, stirring occasionally, until marshmallows are melted and mixture starts to boil. Remove from heat.

Beat cream cheese in a large bowl until smooth. Stir in egg yolk. Fold in 1/3 of the melted marshmallow mixture, then quickly fold in remaining marshmallow until no streaks remain. Stir in lemon juice.

Beat cream in a medium bowl until soft peaks form. Fold into cream cheese-marshmallow mixture until no streaks remain. Spread into graham crust and chill in the refrigerator for 3 hours before serving.