Perfect for a party, this pie can be prepared ahead and kept
covered in the fridge until you're ready to serve it. Take it out
of the fridge 15 minutes before baking and serve it hot for maximum
For olive oil pastry, place flour and a large pinch of salt in a food processor, add butter and process to combine. Add oil and 130ml cold water (you may not need all of it), pulsing between additions, until the dough just comes together. Turn out onto a work surface and knead dough briefly until smooth. Halve dough, wrap each piece in plastic wrap and refrigerate to rest (at least 1 hour or overnight).
Preheat oven to 200C. Heat oil in a small frying pan over medium-high heat, add shallot and fry, stirring occasionally, until softened and golden (5-8 minutes). Transfer to a bowl to cool, then stir in cheeses and oregano and season to taste.
Working quickly, roll out a piece of pastry (keep the other refrigerated) to a rough 20cm x 40cm rectangle. Place on a lightly oiled baking tray, then spread with cheese mixture, leaving a 1cm border. Roll remaining pastry to roughly the same size or a fraction smaller, brush border of base pastry with eggwash, then top with remaining pastry and curl up the sides, pinching all around the edges to seal. Pierce top of pie at regular intervals to allow steam to escape, then brush with eggwash and bake until pastry is set and golden (25-30 minutes; if pie isn’t brown enough, finish it under a hot grill). Sprinkle with sea salt, slice and serve hot.