Prepare Raspberry Mixture:
In a bowl, mix raspberry jam, lemon juice, and half of the raspberries. Lightly mash to combine. Set aside.

Make the Coffee Soak:
In a shallow bowl, combine brewed coffee with raspberry liqueur (if using). Let cool completely.

Whip the Cream:
In a separate bowl, beat heavy cream until soft peaks form.

Make the Mascarpone Filling:
In another bowl, whisk together mascarpone cheese, powdered sugar, and vanilla extract until smooth. Gently fold in the whipped cream until well combined.

Assemble the Tiramisu:
Quickly dip ladyfingers in the coffee mixture and line the bottom of a dish (8×8 or similar). Spread half of the mascarpone mixture over the ladyfingers. Spoon half of the raspberry mixture on top.

Repeat Layers:
Add another layer of dipped ladyfingers, then the remaining mascarpone mixture, followed by the rest of the raspberry topping.

Chill:
Cover and refrigerate for at least 4 hours (or overnight) to let flavors meld and dessert set.

Serve:
Garnish with fresh raspberries, white chocolate shavings, or a dusting of powdered sugar before serving.