01 - Combine flour and salt in a large bowl. Rub cold butter into the mixture until it 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 all liquid has evaporated, approximately 5–7 minutes. Remove from heat and allow to 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 dough on a lightly floured surface to fit the pie dish. Carefully transfer dough to the prepared dish, pressing into the bottom and up the sides. Trim any excess dough hanging over the edges.
07 - Spoon the filling evenly into the pastry shell. Beat the remaining egg and brush the pastry edges with egg wash. Pour any remaining egg over the filling.
08 - Sprinkle the top with additional 2 tbsp grated parmesan. Bake for 40–45 minutes until filling is set and pastry is golden brown. Allow to cool for 10–15 minutes before slicing.