Add the raspberries, sugar, and lemon juice to a saucepan and heat until the raspberries break down and bubble.
Lower the heat and simmer for 23-25 minutes until thickened. Test with a spoon, and cool in the fridge.
In a saucepan, combine sugar, water, and raspberries until dissolved and boiling.
Reduce heat, simmer for 3 minutes, then strain, add limoncello, and cool.
Whisk together mascarpone, powdered sugar, lemon juice, and vanilla until combined.
Gradually add heavy cream and whisk until medium-stiff peaks form.
In a baking dish, spread a little mascarpone mixture.
Dip ladyfingers into raspberry syrup and layer in the dish.
Add half of the mascarpone cream, then half of the raspberry jam.
Repeat layering process and seal with plastic wrap. Chill for at least 8 hours or overnight.
Serve with the remaining raspberry jam and fresh decorations.
