Sprinkle the portobello mushrooms with pepper, salt and a small drizzle of olive oil. Place them on a baking sheet covered with baking paper and bake in the oven for about 15 minutes.
Remove from the oven and let the portobello’s drain well on kitchen paper. A huge amount of moisture always comes out so make sure that it is removed as much as possible.
Heat a frying pan with some olive oil and fry the onion in it until glazy. Add the garlic and fry it for a while.
Add the spinach and let it shrink well. Transfer to a colander/sieve and drain well. Squeeze out any liquid with a spoon.
Now mix the spinach with the grated cheese and fill the portobello shells with it.
Place back on the baking tray and let the cheese melt in the oven. Serve with fresh basil and some more grated Prima Donna.
