Prep the mushrooms by rinsing them under cold water and patting them dry. Slice each mushroom thickly, about ¼ inch, and set aside.

Make the breading mixture by combining all-purpose flour with salt and pepper in a bowl. If using, mix an egg with a splash of milk in a separate bowl.

Coat each mushroom slice in the flour mixture, then dip in the egg mixture (if used), and return to the flour or seasoned breadcrumbs for better coating.

Heat vegetable oil in a large deep pan over medium heat until it reaches about 350°F (175°C).

Fry mushroom slices in small batches for about 3-4 minutes until golden brown, flipping halfway through.

Drain the fried mushrooms on paper towels and serve hot with ranch dressing, garnished with parsley.