Preheat the oven to 180°C.
Lay one pastry sheet flat, brush with melted butter, and sprinkle with half of the caster sugar.
Place the second sheet on top, cut into two rectangles, and move to a baking sheet.
Brush the top with more butter, sprinkle with sugar, and bake for 2 to 4 minutes until golden.
Combine chopped strawberries, icing sugar, and balsamic vinegar in a bowl and soak for 15 minutes.
Blend toffee sauce and half a banana in a food processor until smooth.
Fold the banana mixture into the whipped cream and then gently incorporate the whisked egg whites.
Place banana slices on a baking sheet and sprinkle with caster sugar.
Caramelise the sugar on the bananas using a kitchen blow torch or a hot grill.
Assemble the dessert by layering strawberries, pastry, mousse, and more strawberries on a plate.
Top with the final pastry layer, dust with icing sugar, and garnish with caramelised bananas.