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

In a small saucepan, combine sugar, water, and fresh raspberries. Bring to a boil, stirring until the sugar dissolves. Let it boil for about 3 minutes, then strain to remove seeds.

In a large mixing bowl, combine mascarpone cheese, powdered sugar, lemon juice, and vanilla paste. Beat until creamy and smooth then add heavy cream and whisk until medium-stiff peaks form.

Dip ladyfinger cookies one at a time into the raspberry syrup and layer them with the mascarpone filling in a glass dish. Repeat layers and finish with a mascarpone layer.

Cover the dish tightly with plastic wrap and refrigerate for at least 8 hours or overnight to allow flavors to meld.

Before serving, dollop raspberry jam on top and garnish with fresh raspberries and lemon slices.