01 - Combine flour and salt in a large bowl. Rub in cold butter until mixture resembles coarse crumbs. Add cold water one tablespoon at a time, mixing until dough just comes together. Shape into a disc, wrap in plastic, and refrigerate for 30 minutes.
02 - Preheat oven to 350°F. Grease a 9-inch pie dish with butter or cooking spray.
03 - Heat olive oil in a large skillet over medium heat. Add chopped onion and cook until softened, about 5 minutes. Add minced garlic and cook for 1 additional minute until fragrant.
04 - Add chopped silverbeet to the skillet and cook until wilted and excess liquid has evaporated, about 5 to 7 minutes. Remove from heat and allow to cool slightly.
05 - In a large bowl, combine ricotta, 1/2 cup parmesan, 4 eggs, nutmeg, salt, and black pepper. Mix until well blended, then fold in the cooled silverbeet mixture.
06 - Roll out chilled pastry on a lightly floured surface to fit the pie dish. Carefully transfer pastry to the prepared dish, pressing gently into the bottom and up the sides. Trim any excess dough from the edges.
07 - Spoon the filling evenly into the pastry shell. Beat the remaining egg and brush the pastry edges with it. Pour the remaining beaten egg over the filling.
08 - Sprinkle the top evenly with the additional 2 tablespoons grated parmesan cheese.
09 - Bake for 40 to 45 minutes until the filling is set and the pastry is golden brown. Allow to cool for at least 10 minutes before slicing and serving.