Add the sliced strawberries to a bowl with the sugar, lemon juice, and vanilla. Toss well, then let them sit for 15 to 20 minutes until they look glossy and juicy. You want a syrupy strawberry juice forming at the bottom of the bowl, but the berries should still hold their shape. If they start looking too soft, you’ve gone a little too long, so move on to the next step.

Pour the cold heavy cream into a mixing bowl and whip with the powdered sugar and vanilla until soft peaks form. Add the mascarpone cheese and mix just until the cream becomes thick, smooth, and spoonable. Stop mixing as soon as it holds its shape since overmixing can make mascarpone grainy. The finished cream should look fluffy, not dense.

Spread a thin layer of mascarpone cream on the bottom of an 8×8-inch dish to keep the ladyfingers from sliding. Quickly dip each ladyfinger into the strawberry juices for about 1 second per side, then arrange them in a single layer. The cookies should be lightly moistened, not soaked through, or the tiramisu can turn soggy.

Spread half of the mascarpone cream over the ladyfingers in an even layer. Spoon half of the strawberries over the cream and drizzle just a little of the syrup for flavor. Avoid pouring in too much liquid so the layers stay clean and sliceable.

Add another layer of dipped ladyfingers, then spread the remaining mascarpone cream over the top. Finish with the remaining strawberries, keeping the final topping berry-heavy rather than syrup-heavy for the best texture.

Cover and refrigerate for at least 6 hours, but overnight is best for fully softened layers and clean slices. For neat serving, let it sit at room temperature for about 5 minutes, then cut with a sharp knife wiped clean between slices.