Heat frozen raspberries in a saucepan over medium heat for 5-7 minutes until broken down. Cool, then strain if desired. Refrigerate until completely cool.
Beat cream cheese until fluffy. Add half the powdered sugar, vanilla, and lemon juice, beating until smooth. Mix in cooled raspberry puree.
In a separate bowl, whip heavy cream with remaining powdered sugar until stiff peaks form.
Gently fold whipped cream into raspberry mixture in three additions until uniform in color.
Spoon or pipe into serving dishes and refrigerate for at least 2 hours.
Garnish with fresh raspberries before serving.
Notes
For a smoother texture, strain the raspberry puree to remove seeds.
Use cold equipment to help the mousse set properly.