Preheat the oven according to the puff pastry package directions.
Pinch together the seams and roll out the pastry into a rectangle slightly smaller than your baking sheet. Leaving a margin of about 1/2 inch around the edge, pierce the center of the pastry with a fork in several places.
If time permits, put the pastry on a parchment-lined baking sheet and place it in the freezer for a few minutes to allow the butter to firm up. This helps keep the butter from melting too quickly and creating lopsided pastry.
Bake until golden brown.
While the pastry bakes, make the frosting. Using a stand or hand mixer, cream together the cream cheese and mascarpone. Add the cream and vanilla extract and mix to combine thoroughly. Gradually add the powdered sugar, only adding more when the previous amount is incorporated. Add the salt. More cream can be added if the frosting is too stiff.
While the pastry cools slightly, rinse and hull the strawberries and slice them in half.
Frost the pastry, using the 1/2-inch margin as a boundary. Add the strawberries, sliced side down, covering the pastry.
Garnish with a dusting of powdered sugar and thinly sliced mint leaves, if desired.