Add remaining raspberries to a mixing bowl and top with the lemon and sweetener. Let set for 10 minutes.
Meanwhile, add the cream to a large mixing bowl and beat with an electric mixer until soft peaks form. Beat in the powdered sweetener and vanilla until the cream is as thick as you'd like.
Mash the berries with a fork.
Gently fold the smashed berries into the cream, leaving some streaks of berries in the cream.
Spoon the cream into serving dishes and top with the reserved raspberries.
Notes
I have not tested this raspberry with frozen berries, but I think it would work fine if they were thawed first.Store covered in the refrigerator for 3-4 days.