In food processor, combine flour, butter and salt, and pulse until mixture resembles small peas. With the motor running, drizzle in ice water until dough pulls away from side of bowl.
Transfer dough to a lightly floured work surface. Shape into disc; wrap in plastic wrap. Refrigerate until chilled, 1 hour.
Preheat oven to 350°F.
Filling
Bring a large pot of salted water to a boil. Add rapini and cook for 3 minutes; drain (see note).
In large non-stick skillet, heat oil over medium heat. Add garlic and hot pepper flakes and cook until fragrant, 1 minute. Add reserved rapini and cook, stirring, until coated in oil mixture, 2 to 3 minutes. Season with salt and pepper, remove from heat and let cool.
Roll dough between two sheets of parchment paper into 14-inch (35-cm) circle. Remove top parchment, and slide bottom parchment with dough onto baking sheet.
Arrange rapini in centre of dough, leaving a 1-inch (2.5-cm) border. Fold over pastry edge, partially enclosing filling. Top rapini with provolone. Brush pastry with egg yolk and sprinkle with Parmesan.
Bake until crust is golden brown, 35 minutes. Serve at room temperature.
Notes
You can cook the rapini ahead of time. It will keep in the refrigerator, stored in an airtight container, for up to 3 days.