Dice and salt the aubergines, leaving them to drain in a colander for at least 30 minutes. Heat a large pan (I used a cast iron skillet), over medium high heat until hot. Cook the aubergine in three batches (use 1 tablespoon of oil per batch), stirring often, until the vegetables are dark and caramelised, but not burnt. Season and add to a food processor (or bowl if you don't have one).

Chop the mushrooms as desired and add to the hot pan. Dry sauté in batches until well browned, then add to the aubergines.

Add all the other ingredients, except the halloumi (or sun-dried tomatoes) and walnuts. Pulse in the blender, or mix with a wooden spoon if using a bowl. The processor will make the mixture more homogenous, which I personally prefer, but if you like things chunky you can omit this.

Add the cheese (or sun-dried tomatoes) and nuts, season again if necessary and give it all a final mix with a spoon - do not blend.

Preheat the oven to 200c. Roll out and arrange the bottom layers of pastry, using the butter between the layers - get full directions here. Add the filling. Roll out and arrange the top layers of pastry.

Beat together the egg and Greek yoghurt and brush half of it over the top layer of pastry (or use a soy glaze for vegan). Bake the pie for about 30 minutes, then take it out of the oven, brush with the rest of the glaze and return to the oven for a further 30 minutes. If the pie looks like it is browning unevenly, turn the pie when you add the second layer of glaze.

When the pie is well browned all over, remove from the oven. Can be eaten hot, warm, lukewarm or cold. As with the other pie I posted a few weeks ago, I have said it serves 8 because it slices into that amount of reasonably sized slices, but two slices with some kind of side dish would be a perfectly satisfying meal.