In a medium saucepan over medium heat, combine frozen raspberries, granulated sugar, and lemon juice. Stir occasionally until bubbling, then reduce heat and let simmer for 23-25 minutes until thickened. Cool before refrigerating.

In a small saucepan, mix sugar, water, and a handful of raspberries over medium heat. Bring to a gentle boil, then simmer for about 3 minutes until sugar dissolves and syrup thickens. Strain through a sieve and cool completely.

In a large bowl, mix mascarpone cheese, powdered sugar, lemon juice, and vanilla paste. Whip until smooth. In a separate bowl, beat heavy cream until medium-stiff peaks form, then fold into mascarpone mixture.

Spread a thin layer of mascarpone in the baking dish. Dip ladyfinger cookies in the raspberry syrup briefly, then layer half in the dish, followed by half of mascarpone filling and half of jam. Repeat layers and finish with mascarpone and raspberry jam.

Cover with plastic wrap and refrigerate for at least 8 hours or ideally overnight to meld flavors and set.