Heat oven to 400 degrees. Now cut the onion. Cut about a 1/2 inch off from the non-root end of the onion and peel off the outer later. Turn this side down to help stabilize the onion. Make cuts approximately 1/4 inch apart and 1/2 inch down from the root into the middle of the onion. You don’t want to get too close to the root of the pieces will fall apart too easily.
Pulse Parmesan, BBQ crisps or nut flour if needed and seasoning in a blender until fine powder and then measure out the 2/3 cup. Place foil on a backing sheet and flip you onion over with the root side down. If the onion isn’t staying upright, create a foil ring to set the onion on. Carefully fan out the onion pieces. Using a pastry brush, coat the bottom two layers of onion first then sprinkle on Parmesan/BBQ crisp/Nut Flour seasoning mix. Now do the top pieces in the same manner. Slowly make your way around the onion until all pieces are coated. This will take a bit of time.
Tent onion with the foil and place in the oven for 15 minutes. Un-tent and cook for 10 more minutes. Then re-tent and cook for another 5 minutes until onion is fully cooked.
To make your mayo, you will want an immersion blender.Crack egg into tall jar wide enough to fit your immersion blender. Squeeze in lemon juice. Pour in oil and let egg settle to bottom of jar. Place blender into the jar until it hits the bottom. Blend for 30 seconds then slowly pull the blender up until all the oil is incorporated about 30 more seconds. Make sure you turn the blender off before pulling it out of the jar. You will only need 1/2 of this portion for the recipe. Save the remaining in an airtight container. It is good for a week after the date on your egg carton. Mix all sauce seasoning in with 1/2 cup mayo.