In a saucepan over medium heat, combine raspberries with water. Simmer for about 10 minutes until the berries are soft. Strain the mixture through a fine mesh sieve, returning the juice to the pan. Stir in sugar and lemon juice, simmer for an additional 5 minutes until thickened. Chill the syrup in the refrigerator.

Using a mixer, whip heavy cream on medium-high speed until stiff peaks form, about 3-5 minutes. In another bowl, beat mascarpone cheese with sugar and chilled raspberry syrup along with vanilla extract. Gently fold the whipped cream into the mascarpone mixture.

Quickly dip ladyfingers in the raspberry syrup and lay them in a single layer at the bottom of an 8-inch dish. Spread half of the mascarpone filling over them and grate half of the white chocolate on top.

Repeat the process with another layer of ladyfingers, mascarpone filling, piping any leftover mascarpone decoratively on top, and grating the remaining white chocolate over the dessert.

Cover tightly with plastic wrap and refrigerate for at least 6 hours, preferably overnight, to allow flavors to meld and the tiramisu to set.