Clean the Portobello mushroom caps with a damp cloth, remove the stem and scrape out the gills so you have a well deep enough for the egg.
Rub a little bit of olive oil on the outside of the mushroom to help it cook and keep it from sticking to the pan. Arrange the caps on a baking sheet. Place one slice of prosciutto inside the mushroom cap then top with raw egg. I crack egg in measuring cup as it makes it easy to pour into mushroom.
Sprinkle with black pepper and fresh herbs of choice – I used parsley. (The prosciutto is salty so I don’t recommend adding more.) CAREFULLY place the baking pan into the pre-heated 375 degree F oven and bake for 20-30 minutes. The amount of time required depends on how thick your mushrooms are and how done you like your eggs.