Preheat oven to 350*F and lightly butter or oil a baking dish large enough to hold the chicken breasts in a single layer.
Stir together sour cream, blue cheese, lemon zest, lemon juice, and parsley in a bowl and set aside.
Combine the flour, rosemary, salt and pepper in a shallow dish and stir to mix.
Coat the chicken in the flour evenly, patting to remove excess.
Heat the butter and oil in a large skillet over medium high heat just until it is beginning to brown.
Add the chicken and cook until browned, about 4 minutes per side, without crowding the skillet (cook in batches, if need be).
Transfer the chicken to the baking dish, skin side up if using breasts with skin.
Spread the blue cheese mixture evenly over the chicken.
Combine the bread crumbs with the melted butter and parmesan cheese, stirring to mix.
Sprinkle the mixture evenly over the chicken and bake until the topping is nicely browned and the chicken is cooked through, about 20 minutes (until juices run clear when pierced with the tip of a knife through the thickest part).