Add raspberries and water to a medium saucepan set over medium-high heat.

Use a potato masher or fork to crush the berries as they heat.

Bring the mixture to a simmer, then reduce heat to medium-low and cook for about 2 minutes.

Remove from heat and pour the mixture into a fine-mesh strainer set over a large glass measuring cup.

Press the berries with the back of a spoon or ladle to extract as much juice as possible. Discard the seeds and pulp.

Return the raspberry juice to the saucepan. Add the sugar and lemon juice.

Bring to a boil, then reduce to a gentle simmer and cook for 4–5 minutes, until slightly reduced and syrupy.

Remove from heat and chill in the refrigerator until completely cool.

You should have about 2 cups of raspberry syrup.

To speed cooling, place in the freezer and stir every 10–15 minutes until cool.

In a chilled stand mixer bowl fitted with the whisk attachment, add the heavy cream.

Whip on medium-high speed until stiff peaks form. Transfer the whipped cream to a separate bowl and set aside.

Return the mixer bowl to the stand and switch to the paddle attachment.

Add mascarpone cheese, sugar, ¾ cup of the cooled raspberry syrup, and vanilla extract to the bowl. Beat on high speed until smooth and fully combined.

Add about 1 cup of the whipped cream to the mascarpone mixture and beat briefly to lighten.

Gently fold in the remaining whipped cream with a spatula until the filling is light, fluffy, and uniform.

Pour some of the cooled raspberry syrup into a shallow dish.

Working one at a time, dip each ladyfinger into the syrup until soaked but not falling apart.

Arrange soaked ladyfingers in two neat rows of six along the bottom of an 8-inch square dish.

Depending on the size of your ladyfingers, you may need to trim them. For best results, cut them after dipping so they are softer and less likely to break.

If desired, drizzle 1–2 tablespoons of extra raspberry syrup evenly over the soaked ladyfingers to intensify the flavor.

Spread half of the mascarpone filling evenly over the first layer of ladyfingers.

Using a microplane, fine grater, or zester, grate half of the white chocolate over the filling.

Repeat with a second layer of syrup-soaked ladyfingers.

Spread half of the remaining filling smoothly over the top layer of ladyfingers.

Transfer the rest of the filling to a piping bag fitted with a large round tip (or a zip-top bag with the corner snipped off).

Pipe even rows or dots of filling across the top surface of the tiramisu.

Grate the remaining white chocolate over the top.

Cover the dish tightly with plastic wrap.

Refrigerate for at least 6 hours, preferably overnight, to allow the flavors to meld and the layers to set.

To serve, slice into 9 squares and lift out carefully with a spatula.