Pre-heat the oven to 450˚F.
On a baking sheet, place the mushrooms caps stem side up, drizzle with EVOO and season with salt and pepper. Roast for 10-12 minutes, until tender. Remove from the oven and set aside.
While the mushrooms are roasting, to a food processor add the garlic, onion, EVOO, salt, pepper and nutmeg and pulse to chop. Add the artichokes and cheese and pulse again. Add the spinach and egg yolks, pulse again to combine, then add in the nuts and heavy cream.
Fill the mushroom caps with the spinach-artichoke mixture and bake for another 10-12 minutes, until the filling is cooked through.