1) Place the chicken and buttermilk in a large zip lock bag and coat well. Place in the fridge to sit for at least 4 hours or up to overnight.
2) Preheat the oven to 400 degrees. Line a baking sheet with parchment paper and set aside.
3) In a shallow bowl combine the flour, garlic powder, salt, and pepper. Beat the eggs in a separate shallow bowl and set aside. Add the cornflake crumbs and the parmesan onto a third shallow bowl. Line up the three bowls creating an assembly line. First the flour mixture, then the eggs, then the cornflakes.
4) Working with one at a time, dredge the chicken breasts in the flour, dip into eggs, then dredge in cornflakes, pressing to coat. Make sure to shake off any excess after dipping in each bowl. Place the chicken on the prepared baking sheet and repeat with remaining chicken.
5) Add a small pat of butter on top of each chicken breast. Bake for 12 minutes, then turn chicken over and bake for another 12-15 minutes until chicken is cooked through and golden brown. Garnish each piece of chicken with a slice of lemon and chopped parsley.