Slice the mushrooms to the desired thickness. In a large frying pan heat a large glug of oil (either neutral or olive) over high heat until starting to smoke. Add the mushrooms and season with salt and pepper. Allow to brown and crisp and any released liquid to evaporate. Stir to flip and brown the other side. A pan extremely full of mushrooms will take a very long time to brown; for more even and consistent cooking, fry the mushrooms in batches, or just be prepared to let them go for longer than you think. Conversely, you can also roast mushrooms in a hot (350°F to 425°F [180°C to 220°C]) oven. Fill a roasting dish with mushrooms cut to the desired thickness, dress with a very big glug of oil, and season with salt and pepper. Place in the oven and bake until golden brown and cooked through, stirring every 10 to 15 minutes.