In a medium saucepan over medium heat, combine frozen raspberries, granulated sugar, and lemon juice. Stir occasionally as the mixture simmers for about 10-15 minutes, or until thickened.

In a small saucepan, mix together granulated sugar and water. Bring to a boil, add frozen raspberries, and simmer for about 5 minutes. Strain and allow syrup to cool.

In a large bowl, mix mascarpone cheese, powdered sugar, lemon juice, and vanilla paste until smooth. Fold in whipped heavy cream.

Dip each ladyfinger into the cooled raspberry syrup and layer them in a dish with mascarpone filling and raspberry jam, repeating until completed.

Cover the tiramisu with plastic wrap and refrigerate overnight, ideally for 6-8 hours.

Garnish with raspberry jam and fresh raspberries before serving.