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 soft, about 5 minutes. Add minced garlic and cook for 1 minute more until fragrant.
04 - Add chopped silverbeet to the skillet and cook until wilted and any liquid has evaporated, about 5–7 minutes. Remove from heat and let cool slightly.
05 - In a large bowl, whisk together ricotta, grated parmesan, 4 eggs, nutmeg, salt, and black pepper until well combined. 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 dish, pressing into the bottom and sides. Trim excess dough from edges.
07 - Spoon the filling evenly into the pastry shell. Beat the remaining egg and brush the pastry edges with it; pour the remaining egg over the filling.
08 - Sprinkle the top evenly with 2 tablespoons grated parmesan cheese.
09 - Bake for 40–45 minutes until the filling is set and the pastry is golden brown. Let cool for 10–15 minutes before slicing and serving.