Start by cleaning the mushrooms under cold water to remove any dirt. Trim the stems and pat them dry with a paper towel.
In a large mixing bowl, whisk together the buttermilk and egg until well combined. In a shallow dish, combine the all-purpose flour, salt, and black pepper. In another shallow dish, place the panko breadcrumbs.
Take each mushroom and first dip it into the flour mixture, coating it evenly. Shake off any excess flour, then dip it into the buttermilk mixture, allowing any excess to drip off. Finally, roll the mushroom in the panko breadcrumbs until fully coated. Set aside on a plate.
In your frying pan, pour enough vegetable oil to cover the bottom by about 1 inch. Heat the oil over medium-high heat until it reaches 350°F (175°C).
Carefully place the breaded mushrooms into the hot oil, making sure not to overcrowd the pan. Fry them for about 3-4 minutes on each side, or until they turn a beautiful golden brown.
Once fried, use a slotted spoon to remove the mushrooms from the oil and transfer them to a plate lined with paper towels to drain any excess oil. Serve them warm with your favorite dipping sauce or enjoy them plain.
