With the rack in the middle position, preheat the oven to 375°F (190°C). Line a baking sheet with parchment paper.
On a lightly floured surface, roll out the puff pastry into a 10-inch (25 cm) square. Brush the surface of the dough with the butter and sprinkle with the sugar. Cut into six 3 x 5-inch (7.5 x 13 cm) rectangles. Place the dough on the prepared baking sheet.
Bake for 20 minutes or until golden brown. Let cool completely.
Using a breadknife, cut each puff pastry rectangle in half horizontally and set aside.
In a bowl, whip the cream, icing sugar and vanilla using an electric mixer until stiff peaks form.
Spread the bottom halves of the puff pastry with the jam, then the whipped cream. Freeze for 3 hours or until firm.
Meanwhile, place the chocolate and cream in a bowl. Melt in the microwave oven for 1 minute. Stir until smooth and let cool.
When ready to serve, combine the strawberry slices and sugar in a bowl. Let macerate for 5 minutes. Meanwhile, let the frozen puff pastry sit at room temperature. Spoon the strawberry mixture onto the bottom halves of the pastries, drizzle with the chocolate sauce and top with the other half of the pastry.