From America's Test Kitchen Season 7: Chicken Kiev
We found that butterflying the chicken breasts, then pounding them thin—and even thinner at the edges—helped created chicken bundles that wouldn’t leak the butter filling. Instead of deep-frying the chicken as is traditionally done, we chose to oven-fry the chicken. This made for a crisp, rather than greasy, Kiev. Toasting the bread crumbs prior to breading the chicken helped mimic the flavorful, golden brown crust of the original. All we had left to do was to perk up the plain filling. Traditional recipes stuff the Kievs with butter spiked with nothing more than parsley and chives, but we found that minced shallots were more flavorful than chives and a small amount of minced tarragon added a pleasant hint of sweetness. A squeeze of lemon juice tamed the rich butter with a bit of acidity and Dijon mustard, whisked into the egg wash (for coating the chicken), provided another layer of flavor for a chicken Kiev that was anything but bland.
Unbaked, breaded chicken Kievs can be refrigerated overnight and baked the next day or frozen for up to one month. To cook frozen chicken Kievs, increase the baking time to 50-55 minutes (do not thaw chicken).