Preheat oven to 425F. Line a baking sheet with parchment paper.
Trim the stalks of the mushrooms. If desired, you can scrape out the gills (but I find the mushrooms break easily and doing this doesn’t make much difference). Slice mushrooms 1/4-inch thick.
Put the flour, aquafaba (or other liquid), and panko into shallow plates. Dredge a mushroom slice in the flour, coat with aquafaba, and then press into the breadcrumbs, making sure it’s completely covered. Place on lined baking sheet and repeat with remaining mushrooms.
Bake at 425 until crispy on the outside but still tender inside, about 12-15 minutes. You may turn the fries over halfway through if you want them extra crispy.
Serve with Horseradish Comeback Sauce, below. They also make a great portobello burger.
Aquafaba is the liquid from cooked or canned beans (usually chickpeas). It makes a great substitute for egg in this recipe, especially if you let it refrigerate it beforehand (it's thicker and more egg-like cold). Soy milk, almond milk, and other non-dairy milks also work, but they work better with a little flax seed meal added to make them thicker. Try adding 1/2 teaspoon of ground flax and allow to thicken for a few minutes.If your bread crumbs are seasoned, use less Creole seasoning to avoid over-salting.