Preheat oven (electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer). Roll out puff pastry. Cut dough sheet crosswise into 3 strips (each approx. 14 x 24 cm). Prick several times with a fork. Remove the strips of dough from the paper and place them next to each other on a baking tray lined with baking paper. Bake in a hot oven for about 20 minutes until golden brown.
Soak the gelatine. Wash and clean the strawberries. Finely puree 100 g strawberries. Mix mascarpone, strawberry puree, sugar and 3 tablespoons lemon juice. Squeeze the gelatine and dissolve at low heat. Stir in 2 tbsp. cream, then stir into the rest of the cream. Whip cream until stiff, fold in. Chill the cream until it begins to gel.
Let the puff pastry bases cool down. Cut the remaining strawberries into slices. Spread the cream on 2 pastry bases, approx. 1⁄3 each, and cover each base with strawberries. Spread the rest of the cream thinly on the berries, place the bases on top of each other. Cover with the 3rd cake base.
Stir icing sugar and 1 tablespoon lemon juice until smooth. Dribble the icing over the top cake base. Chill the cake for about 2 hours. Cut into pieces.