In a small bowl, combine panko breadcrumbs with Old Bay seasoning, marjoram, garlic powder, kosher salt, and fresh ground black pepper. Mix well.

In another bowl, pour in the buttermilk and let it sit nearby for easy access.

Gently rinse the mushrooms under cold water and dry them thoroughly using a clean kitchen towel.

Place the mushrooms in a zipper bag with flour, seal, and shake to coat evenly.

Dip each floured mushroom in the buttermilk, letting excess drip off, then roll in the breadcrumb mixture.

Heat vegetable oil to 375°F in a Dutch oven.

Carefully place the breaded mushrooms in the hot oil in small batches and fry for about 2-3 minutes until golden brown.

Use a slotted spoon to remove the mushrooms and transfer them to a plate lined with paper towels to drain excess oil.

For an air-fried version, preheat your air fryer to 375°F and cook the coated mushrooms for 5-7 minutes.