For the crust: Mix flour, processed almonds, sugar and salt. Rub in the butter until the mixture is crumbly. Add the egg yolk and form the dough. If needed, add 1 tbsp of cold water at a time. Shape into a flat disc and wrap in plastic wrap. Chill for 30 minutes.
In another bowl, combine the sliced peaches, sugar, lemon juice and cornstarch.
Preheat oven at 190°C/370°F. Roll out the dough into a circle on parchment paper and place it on a baking sheet. Place the peaches in the center leaving a 1-inch border. Fold up the edges of the dough around the filling, and gently pleat to seal. Optional: brush the edges with egg wash and sprinkle with sugar.
Bake for 30 minutes or until golden. Serve warm with whipped cream or ice cream.
