Heat oil in a fry-safe pot over medium-high heat (about 375 degrees).
Optional: Turn oven to 220 degrees (to keep chicken warm while you prepare McGriddles)
Prepare a surface to place the finished fried chicken - a cooling rack beside the stove, lined with layers of paper towels or brown bags.
In a small bowl, combine the beaten egg and water. Mix well.
In a ziplock bag or shallow bowl, add all dry ingredients (flour, cornstarch and seasonings)
Place the prepared chicken fillets into the flour mixture to coat thoroughly, dip into the egg wash, and then back into the flour mixture. Ensure all of the surface area of the chicken fillets are covered in batter.
Fry the chicken in batches as to not overcrowd the pan, adjusting the temp as needed to maintain temperature.
When chicken is near cooked (about 6-7 minutes), remove from the pot and place onto prepared surface. Allow it to cool for just a minute or so and place back into the pan for an additional 1-2 minutes. Remove from the frying oil and allow to cool.
Optional: place chicken into the oven to stay warm while preparing the McGriddles.