1. Preheat the oven to 425°F. Line a large rimmed baking sheet with parchment paper. 

2. Roll out the pastry on a lightly floured counter, using a lightly floured rolling pin, into a 14-inch circle. Loosen the pastry from the counter by gently sliding a thin metal spatula underneath it, then transfer to the prepared baking sheet. 

3. Pit the plums and slice each one into 6 to 8 wedges. You should have about 8 cups. Whisk the sugar and corn starch together in a large bowl, then add the plums. Drizzle with almond extract, then stir everything together. It will be a bit messy and clumpy, but don’t worry. 

4. Pile this mixture into the middle of the pastry and smooth it out, leaving a 2-inch border. Fold the pastry border up over the filling, pleating as necessary. 

5. Bake 15 minutes. Reduce heat to 350°F and bake another 20 to 25 minutes or until the crust is golden and the filling is very bubbly. Let stand at least 1 hour before serving.