Preheat oven to 425°F. Line a baking sheet with foil for easy clean-up.
In a small bowl, mix together mayonnaise and sour cream. In another small bowl, combine Parmesan, bread crumbs, and garlic salt.
Lay chicken breasts on baking sheet. Spread 1/4 mayonnaise mixture on top and down sides of each chicken breast. Sprinkle 1/4 of Parmesan/bread crumb mixture on top of each chicken breast, covering and lightly pressing it into the mayonnaise mixture.
Bake for 20 minutes or until chicken is cooked through, taking care not to overcook.
For a dairy-free version, you may use all mayonnaise (in lieu of half sour cream/yogurt).
If you don't have Panko bread crumbs, regular bread crumbs (plain or seasoned) will work perfectly fine. I just like Panko because they're extra crunchy.
This chicken turns out really moist and juicy, as long as you're careful not to overcook it! If you're worried about overcooking, insert a meat thermometer into the thickest part of a breast and remove the pan from the oven when it reaches 165°F.