Step 1: Make the Raspberry Jam
In a medium saucepan, combine raspberries, sugar, and lemon juice. Heat on medium until the berries break down and the mixture begins to bubble.

Reduce to a simmer and cook for 23–25 minutes, mashing the berries occasionally. The jam is ready when it thickens and leaves a clear line on the back of a spoon.

Transfer to a shallow dish and cover with plastic wrap. Chill until room temperature or cooler—about 1 hour.

Step 2: Prepare the Raspberry Syrup
In a small saucepan, combine sugar, water, and raspberries. Heat until the sugar dissolves and the mixture boils.

Reduce to a simmer for 3 minutes, stirring and breaking down the berries.

Strain through a fine mesh sieve into a bowl. Discard seeds. Add limoncello (if using) and let cool to room temperature.

Step 3: Whip the Mascarpone Cream
In a large bowl, beat mascarpone, powdered sugar, lemon juice, and vanilla paste until smooth—about 30 seconds.

Scrape down the bowl and add cold heavy cream. Beat on medium-high until the mixture forms medium-stiff peaks. Don’t overwhip.

Step 4: Assemble the Tiramisu
Spread a thin layer of mascarpone filling in the bottom of your dish.

Dip ladyfingers into the raspberry syrup twice—quickly on each side—and layer in the dish.

Spread half of the mascarpone cream over the ladyfingers. Smooth with a spatula.

Top with half of the chilled raspberry jam and spread gently.

Repeat the process: syrup-soaked ladyfingers, remaining mascarpone, and then cover with plastic wrap.

Chill for at least 8 hours or overnight.

Step 5: Finish and Decorate
Just before serving, top with the remaining raspberry jam. Decorate with fresh raspberries and thin lemon slices.

Slice and serve cold. For clean slices, use a thin knife dipped in warm water.