In a medium sauce pan, combine raspberries and ½ cup sugar, and mash them together with a spatula. Cook stirring occasionally until it reaches jam consistency. Remove from heat and pour through a strainer, pushing on the back with a spatula to get all of the juice possible. Stir in lemon juice and gelatin. Pour back into saucepan and place over medium heat, whisking until gelatin dissolves and mixture is hot (not boiling). Remove from heat and pour into another bowl to cool to room temperature. Watch carefully because once it cools, it will thicken and become difficult to blend.

Whip heavy cream with powdered sugar on high speed until it forms peaks. Gently fold in raspberry sauce. Cover, or transfer to piping bag, and refrigerate 3 hours or overnight.