Portabella mushrooms have a large, flat cap that is excellent for grilling and eating in place of a hamburger patty or steak. Portabella mushrooms are high in potassium, riboflavin and niacin. Replacing a meat entree with a portabella greatly reduces your intake of fat, calories and cholesterol. You can recreate the flavor of a grilled portabella using your oven's broiler. Serve broiled portabellas alone, drizzled with vinaigrette or sandwiched between two hamburger buns with or without cheese and other burger condiments.
Rub the top of the portabella with a damp paper towel to remove dirt.
Pull off the portabella's stem and keep it in a paper bag in the refrigerator for up to a week to use later in another mushroom dish, such as stuffed mushrooms.
Place the top rack in the oven 4 to 6 inches below the top heating element so that the element will broil the mushroom perfectly without burning.
Preheat the broiler setting on your oven to 500 degrees Fahrenheit.
Brush the mushroom cap with melted butter or olive oil, using a pastry brush.
Assemble a broiler pan, placing the slatted rack on top of the rimmed baking sheet.
Place the portabella on the broiler pan and slide the pan onto the top rack in the oven. Close the oven and cook for four to six minutes.
Pull the pan out of the oven and use tongs to flip the mushroom over. Paint the second side of the mushroom with butter or olive oil and return the sheet to the broiler. Close the oven and cook for another four to six minutes.
Test the mushroom for doneness by poking the cap with a fork. When done, the mushroom will be tender and juicy.
Remove the portabella from the oven and serve warm, sliced and drizzled with vinaigrette, or whole, topped with cheese and served on a hamburger bun.