Vegetarian Mushroom-Spinach Pastitsio

prepare filling

1. Preheat oven to 180°C (350°F). Prepare a 23x33 cm (9x13 in) baking dish and lightly oil it.
2. Heat 1 tbsp olive oil in a large skillet over medium heat. Add chopped onion and sauté until translucent, about 5 minutes.
3. Add minced garlic and sliced mushrooms; cook until mushrooms release liquid and it evaporates, about 8–10 minutes.
4. Stir in tomato sauce, dried oregano, salt and pepper. Simmer gently 6–8 minutes to concentrate flavors.
5. Add chopped spinach in batches, stirring until wilted and excess liquid evaporates. Taste and adjust seasoning; set filling aside.

cook pasta & make béchamel

1. Bring a large pot of salted water to a boil. Par-boil pasta sheets 2–3 minutes if required by package, or cook until just al dente; drain and toss with 1 tbsp olive oil to prevent sticking.
2. To make béchamel, melt butter in a saucepan over medium heat. Whisk in flour and cook 1–2 minutes without browning.
3. Gradually whisk in milk, smoothing lumps, and simmer until thickened, about 6–8 minutes. Season with salt, pepper and nutmeg.
4. Remove béchamel from heat and, if using, whisk in the egg quickly to enrich, then stir in grated kefalotyri or Parmesan until combined.

assemble & bake

1. Spread a thin layer of tomato-mushroom filling on the bottom of the prepared dish to prevent sticking.
2. Layer half the pasta sheets to cover the base, then spread half the vegetable filling evenly over them.
3. Add remaining pasta sheets in a single layer, top with remaining filling, then pour the béchamel sauce evenly over the top, smoothing with a spatula.
4. Sprinkle crumbled feta evenly over the béchamel and a little black pepper.
5. Bake in the preheated oven for 35–40 minutes until the béchamel is set and golden brown on top.
6. Let rest 10–15 minutes before slicing so layers firm up; serve warm with extra crumbled feta if desired.