01 -
Add raspberries, sugar, and lemon juice to a saucepan over medium heat. Heat until raspberries thaw, break down, and bubble. Lower to a simmer, stir occasionally, and mash down the raspberries. Let it simmer for 23–25 minutes until thickened. Test by drawing a line on the back of a spoon without it moving. Transfer to a shallow bowl, cover with plastic wrap, and cool in the fridge to room temperature or colder (about 1 hour).
02 -
Combine sugar, water, and raspberries in a small saucepan over high heat until sugar dissolves and boils. Reduce to a simmer for 3 minutes, stirring and mashing the berries occasionally. Strain the syrup using a fine-mesh sieve, discarding raspberry kernels. Stir in limoncello if desired and let cool to room temperature.
03 -
Using a hand mixer or stand mixer with a whisk attachment, combine mascarpone, powdered sugar, lemon juice, and vanilla paste until smooth (about 30 seconds). Scrape the bowl, add heavy cream, and whisk until medium-stiff peaks form.
04 -
Using a 27x20 cm or 23x23 cm baking dish, spread a thin layer of mascarpone cream at the bottom. Dip ladyfingers into raspberry syrup twice on each side and layer them in the dish. Spread half the mascarpone cream evenly, then half the raspberry jam. Repeat the process without topping with raspberry jam. Cover with plastic wrap and refrigerate for at least 8 hours, preferably overnight.
05 -
Before serving, spread the remaining raspberry jam on top in an even layer. Optionally, decorate with fresh raspberries and lemon slices.