Combine the almond flour, sweetener or sugar (if using) and salt in a food processor. Pulse to combine. Add the diced butter and pulse only a couple of times to evenly disperse the butter until the mix resembles fine crumbs. Add the egg and vinegar, pulsing a few times until a dough forms. Turn out into a bowl; knead gently to create a mound; wrap the dough in plastic wrap and chill in the refrigerator for at least 30 minutes to an hour.
In a small bowl mix the sliced peaches, vanilla and sweetener (or sugar).
Preheat the oven to 190°C | 385°. Line a baking try with parchment/baking paper.
Remove dough from the refrigerator once chilled and press out with your hands onto the baking tray (into a circle or rectangular shape) to desired size, about 1/4-inch thick. (Don't roll it. It's not as pliable as flour dough. Don’t worry about being neat, rustic looks good too!)
Arrange the peaches in the centre of your dough, leaving 1 1/2-inches of dough surrounding the peaches. Gently fold up the outside border around the peaches, pressing and moulding it with your finger tips as you go. Brush the top of the crust with the melted butter; sprinkle with the almonds,
Bake for 30-40 minutes or until the dough changes to a deep golden colour and the fruits juices are bubbling.
Remove from the oven and allow to cool. Serve with the Mascarpone cream