Preheat your oven to 200 degrees. Lightly grease a 20cm sandwich tin with butter.
Peel and chop the butternut squash into chunks. Place onto a baking sheet, add the olive oil and a generous pinch of salt and pepper. Toss to coat well. Place in the oven and roast for 45 minutes until softened.
Meanwhile, heat some olive oil in a saucepan. Add the rocket and spinach (you may need to do this in batches) and stir-fry until completely wilted. Allow cooling before handling. Place into a clean tea towel and squeeze out the moisture. Add to a bow.
Once the squash has been roasted, add to the same bowl. Pull the cheese into chunks and add to the bowl along with the eggs. Season well and mix until everything is well incorporated.
Melt butter in a saucepan. Unroll the sheets of pastry and paint a sheet in melted butter. Lay the sheet butter side up into the tin allowing the excess to overlap the sides. Repeat with the rest of the sheets, layering at different angles, until the tin is completely covered.
Pile the tin with the filling squashing it down lightly. Fold the surplus of the pastry until everything is completely covered. Paint the remaining butter over the pastry. Bake for 30 minutes, until the top, is lightly golden and crispy.
Allow the pie to cool for 30 minutes before serving. This can be eaten hot or cold so it's ideal for leftovers.