Prepare the Raspberry Jam:

• In a saucepan, combine raspberries, sugar, and lemon juice. Heat over medium heat until the mixture bubbles, then reduce to a simmer for 23-25 minutes until thickened.
• Transfer to a shallow bowl, cover, and refrigerate until cooled to room temperature, about 1 hour.

Prepare the Raspberry Syrup:

• In a small saucepan, combine sugar, water, and raspberries. Bring to a boil over high heat, then reduce to a simmer for 3 minutes, mashing the berries.
• Strain through a fine mesh sieve to remove seeds, discard solids, and let the syrup cool to room temperature.
• Optional: Stir in limoncello for added flavor.

Prepare the Mascarpone Filling:

• Using an electric mixer, beat mascarpone, powdered sugar, lemon juice, and vanilla extract until combined, about 30 seconds.
• Add heavy cream and whip until medium-stiff peaks form.

Assemble the Tiramisu:

• In a serving dish, spread a thin layer of mascarpone cream on the bottom.
• Quickly dip ladyfingers into the raspberry syrup, ensuring each side is moistened, and arrange half in a layer over the cream.
• Spread half of the mascarpone mixture over the ladyfingers, smoothing into an even layer.
• Dot half of the raspberry jam over the mascarpone and gently spread.
• Repeat the layers: dip remaining ladyfingers, add mascarpone, and dot with the remaining jam.
• Cover and refrigerate for at least 8 hours or overnight.

Serve:

• Before serving, spread the reserved raspberry jam over the top layer.
• Garnish with fresh raspberries and lemon slices.
• Slice and enjoy!