Make strawberry sauce: In a small mixing bowl, stir together ⅓ cup strawberry jam, 3 Tablespoons water, and 1 Tablespoon lemon juice until well combined.
Make filling: In a medium sized mixing bowl, beat together 8 ounces mascarpone cheese, ½ cup heavy cream, ½ cup sugar, ½ teaspoon vanilla and 1 teaspoon lemon zest. Beat for about 2 minutes, until it's thick and creamy and the consistency of whipped cream.
Dip cookies: Dip 12 ladyfinger cookies one at a time in the strawberry sauce and lay in a single layer in a 8x8 square baking dish (or similar sized serving dish.)
Spread cream and strawberries: Spread half of the creamy filling over the ladyfingers. Spread out half the sliced strawberries on top of the cream.
Make a second layer: Repeat the first layer by dipping and spreading the cookies, followed by the filling and the strawberries.
Cover and chill: Cover with plastic wrap and refrigerate for at least 8 hours.
