Prepare Strawberries. Slice half of your strawberries for layering. Puree the remaining strawberries with sugar and lemon juice until smooth. Stir in strawberry jam if using for extra sweetness.
Make Mascarpone Cream. In a bowl, beat heavy cream until stiff peaks form. In another bowl, whisk mascarpone with vanilla and sugar until smooth. Gently fold whipped cream into mascarpone until fully combined.
Dip Ladyfingers. Quickly dip each ladyfinger into cooled espresso or strong coffee. Do not oversaturate to maintain structure.
Layer the Dessert. In a 9x13 inch dish, spread a thin layer of mascarpone cream. Add dipped ladyfingers in a single layer. Top with half the strawberry puree, half the sliced strawberries, and half of the mascarpone cream. Repeat with another layer of dipped ladyfingers, remaining puree, strawberries, and mascarpone cream.
Chill. Cover and refrigerate for at least 4 hours, preferably overnight for best flavor melding.
Serve. Dust with powdered sugar and garnish with fresh mint and extra strawberries before serving.