Preheat Air Fryer or oven to 375F. If using, roughly chop mushrooms into ½-inch pieces and place in large pan heated to medium low. Sprinkle with ½ teaspoon salt.
In a small bowl or glass measuring cup, pour olive oil, parsley, 15 drops Black Truffle flavouring, and 10 drops Pesto flavouring. Drizzle 2 tablespoons flavoured oil over mushrooms (if making). Cook until they are browned and release most of their moisture, stirring occasionally, approximately 15-20 minutes. You are looking for them to be quite dry in the pan and feel a little chewy.
While mushrooms are cooking, place fries in a large bowl and toss with remaining flavoured olive oil. Air-fry for 10mins. If baking in the oven, place on a large baking tray in a single layer and bake for 12 minutes.
While fries are cooking, Combine mayonnaise, remaining 15 drops Black Truffle flavouring, ½ teaspoon salt, pepper, lemon juice, and half of the grated Parmesan cheese in a small bowl.
After 10-12 minutes of cooking fries, or when fries feel slightly crisp but not browned, remove from air-fryer or oven, toss fries in bowl with half of truffle mayo mixture. Place back in air-fryer or oven for an additional 5-8 minutes depending on how crispy you like your fries.
Place fries on a platter topped with chewy truffle mushrooms (if using) and remaining cheese. Serve remaining mayonnaise on the side as a dip or drizzled on top.