Pour the oil into a medium pot so that it’s 2-3 inches deep. Place the pot over medium-high heat and start to bring the temperature to 325-350°F (165°C).
Rinse the mushrooms and pat them dry as much as possible. Add the mushrooms and cornstarch to a bag or bowl with a lid. Shake the bowl around to coat the mushrooms with the cornstarch. It’s okay if they aren’t entirely covered.
Stir the wet batter ingredients into a thick slurry in a shallow bowl. Combine the dry breading ingredients in a separate shallow bowl.
Dip each mushroom into the wet batter until it’s fully coated. I use a fork for this. Give it a gentle shake to shake off some of the excess batter and then place it in the dry bowl.
Roll each mushroom into the dry breading until all of the wet batter is covered with it. I use a slotted spoon for this. Repeat these steps until all of the mushrooms are breaded. Note, the wet batter will thicken over time. Stir in 1-2 tablespoons of water or plant milk to loosen it up and thin it out, if needed.
Fry the mushrooms in small batches for 3-4 minutes, flipping them halfway through. Remove them from the hot oil with a skimmer when they are golden brown.
Place them on a wire rack to cool and for the excess oil to drip off. Make sure to let them cool for at least 5 minutes because the center will be hot! Garnish the breaded mushrooms with fresh herbs such as basil and enjoy!