From the New York Times

The simplest way to keep breast meat moist and make it flavorful is to put fat and flavor inside — to stuff it. At its simplest, this means cutting a slit in bone-in chicken breasts and spreading a little butter or drizzling a little olive in the incision, an undemanding task that improves the meat’s flavor and texture immensely. When you mix the butter with fresh tarragon, basil, chives, roasted garlic or whatever other flavoring you like, you upgrade the results significantly.