Step 1: Prepare the White Chocolate Cream

1. In a large bowl, whip the heavy cream and powdered sugar until soft peaks form.
2. Add the mascarpone and vanilla extract, mixing gently until smooth.
3. Fold in the melted white chocolate until fully incorporated. Set aside.

Step 2: Make the Raspberry Sauce

1. In a saucepan over medium heat, combine raspberries, sugar, and lemon juice.
2. Cook for about 5 minutes, stirring occasionally, until the raspberries break down.
3. Strain through a sieve to remove seeds and let it cool.

Step 3: Assemble the Tiramisu

1. Lightly dip each ladyfinger into raspberry juice or white chocolate liqueur (if using).
2. Arrange a layer of soaked ladyfingers in a serving dish.
3. Spread half of the white chocolate cream over the ladyfingers.
4. Drizzle some raspberry sauce over the cream.
5. Repeat the layers, finishing with a layer of white chocolate cream.

Step 4: Chill and Serve

1. Cover the tiramisu and refrigerate for at least 4 hours (overnight is best).
2. Before serving, garnish with fresh raspberries, white chocolate shavings, and powdered sugar.
3. Slice and enjoy this luxurious dessert!