01 - Combine flour and salt in a large bowl. Rub in cold butter until mixture resembles coarse crumbs. Gradually 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. Generously 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, about 5 to 7 minutes. Remove from heat and allow to cool slightly.
05 - In a large bowl, combine ricotta, grated parmesan, 4 eggs, nutmeg, salt, and black pepper. Mix thoroughly, then stir in the cooled silverbeet mixture until evenly distributed.
06 - Roll out chilled pastry on a lightly floured surface to fit the pie dish. Carefully transfer dough to the prepared dish, pressing gently into the bottom and up the sides. Trim excess dough from edges.
07 - Spoon filling evenly into the pastry shell. Beat remaining egg and brush over pastry edges. Pour remaining egg over the filling surface.
08 - Sprinkle 2 tablespoons grated parmesan evenly over the top. Bake for 40 to 45 minutes until filling is completely set and pastry is golden brown. Allow to cool for at least 10 minutes before slicing.