Add the raspberries, sugar, and lemon juice to a saucepan and heat until the raspberries are no longer frozen and have started to break down. Stir occasionally and mash down raspberries with a rubber spatula.

Let it simmer for 23-25 minutes or until the raspberry jam has thickened. Cool the jam in a shallow bowl in the fridge until room temperature.

While the jam cools, make the syrup by boiling the sugar, water, and raspberries in a saucepan until the sugar dissolves.

Reduce the heat and simmer for 3 minutes. Strain the syrup into a bowl, discard the kernels, and add limoncello to cool.

Cream the mascarpone, powdered sugar, lemon juice, and vanilla paste until combined. Add heavy cream and whisk until medium-stiff peaks form.

In a 27x20 cm or 23x23 cm baking dish, spread a little mascarpone cream at the bottom. Dip lady fingers in raspberry syrup and layer them in the dish.

Add half of the mascarpone cream, followed by half of the raspberry jam. Repeat the process and allow to set covered in the fridge for at least 8 hours.

Before serving, add the remaining raspberry jam and optionally decorate with fresh raspberries and lemon slices.