Step 1: Prepare the Raspberry Syrup

1. In a saucepan over medium heat, combine raspberries, sugar, and water.
2. Simmer for about 5 minutes, stirring occasionally until the raspberries break down.
3. Strain the mixture through a fine-mesh sieve to remove seeds.
4. Stir in lemon juice and set aside to cool.

Step 2: Make the White Chocolate Mascarpone Filling

1. Melt the white chocolate in a microwave-safe bowl in 30-second intervals, stirring in between. Let it cool slightly.
2. In a mixing bowl, beat the mascarpone cheese, powdered sugar, and vanilla extract until smooth.
3. In a separate bowl, whip the heavy cream until stiff peaks form.
4. Gently fold the melted white chocolate into the mascarpone mixture, then fold in the whipped cream until fully combined.

Step 3: Assemble the Layers

1. Quickly dip each ladyfinger into the raspberry syrup and arrange a single layer in the bottom of an 8×8-inch dish.
2. Spread half of the mascarpone mixture over the ladyfingers.
3. Sprinkle fresh raspberries over the mascarpone layer.
4. Repeat with another layer of dipped ladyfingers, mascarpone cream, and raspberries.

Step 4: Chill for the Best Flavor

1. Cover and refrigerate for at least 4 hours, preferably overnight, to let the flavors meld.
2. Before serving, garnish with white chocolate shavings and a dusting of powdered sugar or cocoa powder.