In a medium saucepan over medium heat, combine frozen raspberries, granulated sugar, and lemon juice. Allow to simmer for 23-25 minutes until thickened.

In another saucepan, combine sugar, water, and a handful of raspberries. Bring to a boil, then simmer for 3 minutes and strain.

In a large bowl, whip mascarpone with powdered sugar, lemon juice, and vanilla until smooth. Fold in whipped cream gently.

Dip ladyfingers in raspberry syrup and layer in a baking dish with half the mascarpone filling and some raspberry jam.

Cover and refrigerate for at least 8 hours, preferably overnight. Top with jam, raspberries, and lemon slices before serving.