• Preheat the oven to 400°F/200°C.

To make the filling

• Peel, core and cut the apples into small pieces of equal size. Place in a saucepan with sultanas, sugar, cinnamon, vanilla and lemon juice. Cook over medium heat for 10 minutes, stirring occasionally or until the apples are just tender. Remove from heat and place in a heatproof bowl; add cornstarch to the hot apple mixture, stirring as you do. Set aside to cool.
  

To assemble

• Place the puff pastry sheet onto a lightly floured piece of parchment paper and use a lightly floured rolling pin to roll it to a ~30cm x 35cm (12 x 14 inch) rectangle.
• Mark the puff pastry into three equal parts lengthways. Cut the top corners off (triangle shape), then cut notches in the bottom. This allows you to fold over the pastry for a much more finished look. The center of the pastry will hold the filling, and the sides will be flipped over. Use a knife to cut slating strips approximately 1-inch in width down both sides of the pastry. Spoon half of the filling down the center, leaving space at the top and bottom ends.
  
• Fold both ends at the top and bottom over the filling to prevent the filling oozing out when baking.
  
• Braid the pastry by crossing the strips over the filling overlapping each other.
  
• Trim any loose ends and transfer to a baking sheet. Repeat the process with the second sheet of puff pastry.
  

To finish and bake

• Brush the strudel with plant-based milk and bake until golden brown, 25 to 30 minutes. Remove from the oven and cool before slicing and serving.