Fill a large pot with 5 liters of water and cook on high heat.
Once the water starts boiling, add 35 g salt and the MISKO Rigatoni Small. Stir with a spoon and let the pasta boil for 2 minutes less than the time indicated on the package.
Strain the pasta and sprinkle with 2 tbsp. olive oil. Gently stir and place it in a lightly oiled heat resistant dish or pan.
In a shallow pot, heat up 3 tbsp. olive oil and sauté the onion for 2-3 minutes until it softens.
Add the mushrooms, salt and freshly ground pepper, and sauté for 5-7 minutes until most of the liquid evaporates.
Add the spinach in 2-3 batches (in case it does not fit in one single batch) and saute for 3-4 minutes, until tender. Remove from the heat and allow the vegetables to cool for 10 minutes.
In a bowl, mix the whipping cream with the Feta cheese, half the Graviera cheese and the nutmeg and pour the mixture into the pan.
Add the vegetables from the pot and stir gently with a spoon so the ingredients are uniform. Sprinkle with the rest of the Graviera cheese and the bread crumbs.
Bake the pasta in a preheated oven at 180°C for approximately 30 minutes, until the cheese has melted and is golden brown.
Allow the food to rest for 10-15 minutes and then serve.