Thaw pastry sheet at room temperature for about 30 minutes (should still be cold when using). Preheat oven to 400 degrees F.
Unfold the pastry on a lightly floured surface and cut along the 2 fold lines (will have 3 strips). Cut each strip into 3 squares and place 2-inches apart on an ungreased baking sheet. Bake for 10-15 minutes, or until golden brown. Remove from the baking sheet and place pastry squares onto a wire rack.
Beat together the heavy cream, sugar, and vanilla extract in a chilled bowl until stiff peaks form; set aside.
In a separate bowl, whisk together vanilla instant pudding mix and milk for 1-2 minutes, or until thickened. Scoop the pudding into the cream mixture and gently fold in until completely mixed.
Cut each of the pastry squares into 2 slices and set aside the 9 top halves. Place the 9 bottom halves on a clean tray or a large plate. Spread about 2-3 tablespoons of the cream filling onto each. Top with a single layer of strawberry slices and top with the 9 top halves of the pastry squares.
Scoop a small dollop of the cream filling on each napoleon and gently press a small strawberry wedge into each cream dollop.
Serve immediately or store in the fridge for up to a day or 2.