1. Add the frozen raspberries, sugar, and lemon juice to a saucepan and heat until the raspberries thaw and the mixture begins to bubble. Reduce to a simmer, stirring occasionally and mashing the berries.

2. Simmer for 23–25 minutes until the mixture thickens into jam. Test by drawing a line through a spoonful with your finger—if it holds its shape, it is ready. Transfer to a shallow bowl and refrigerate until cooled.

3. To make the syrup, combine sugar, water, and raspberries in a small saucepan over high heat until the sugar dissolves and the mixture boils.

4. Reduce heat and simmer for 3 minutes, breaking down the berries as it cooks. Strain through a fine mesh sieve and discard seeds. Stir in the limoncello and allow the syrup to cool.

5. In a mixing bowl, beat mascarpone, powdered sugar, lemon juice, and vanilla paste until smooth and combined.

6. Add the cold heavy cream and whip until the mixture forms medium-stiff peaks.

7. Spread a thin layer of mascarpone cream on the bottom of a baking dish.

8. Dip ladyfinger cookies briefly into the raspberry syrup and arrange them in a single layer in the dish.

9. Spread half of the mascarpone cream over the ladyfingers, then add half of the raspberry jam and smooth evenly.

10. Repeat with another layer of syrup-dipped ladyfingers and the remaining mascarpone cream.

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

12. Before serving, spread the remaining raspberry jam on top and garnish with fresh raspberries and lemon slices if desired.