Preheat the oven to 400°F. Place each pastry sheet on a lined baking tray and bake until golden and crisp, about 12 to 15 minutes. Let cool completely.
In a saucepan, heat the almond milk, heavy cream, sweetener, butter, vanilla, and salt until steaming. Whisk the egg yolks and cornstarch in a bowl. Slowly add some hot milk mixture to the egg yolks, then return everything to the pan. Cook, whisking constantly, until thick and smooth.
Place one pastry sheet in the bottom of a lined square or rectangular pan. Spread the warm custard over it. Top with the second pastry sheet and press gently.
Whip the heavy cream with sweetener and vanilla until soft peaks form. Spread over the top pastry layer.
Refrigerate for at least 2 hours before slicing. Dust with powdered sugar-free sweetener before serving.
