Make the herbed butter: in a bowl, soften the Unsalted Butter and stir in finely chopped Parsley, chopped Dill, minced Garlic, a little Lemon Juice, and a pinch of Salt and Black Pepper to taste.
Shape the butter into a log (about 1–1.5 inches thick), wrap tightly in plastic wrap, and freeze or chill until firm, about 30 minutes.
Prepare the chicken: place each Boneless Skinless Chicken Breast between plastic sheets and pound gently to an even thickness (about 1/4–1/2 inch), being careful not to tear the meat.
Season both sides of the flattened chicken with additional salt and pepper to taste.
Cut the chilled butter log into portions and place one portion in the center of each chicken breast, then fold the edges up and around the butter, sealing well; use toothpicks if needed to secure the seam.
Set up a dredging station with three shallow dishes: one with All-Purpose Flour seasoned with a little salt and pepper, one with beaten Eggs, and one with Breadcrumbs (season the crumbs lightly with salt and pepper).
Dredge each stuffed breast first in flour, shaking off excess, then dip in the beaten egg, and finally coat thoroughly with breadcrumbs. For an extra-crispy crust, repeat the egg and breadcrumb step once more.
Chill the breaded chicken in the fridge for at least 20 minutes to help the coating adhere and to keep the butter cold inside.
To cook on the stovetop: heat about 1/4 inch of Sunflower Oil in a large skillet over medium heat until shimmering. Fry the kievs 3–4 minutes per side until golden brown, then lower the heat and cook another 6–8 minutes, turning occasionally, until cooked through (internal temperature 165°F / 74°C). To finish in the oven, transfer the skillet to a preheated 375°F (190°C) oven and bake 10–12 minutes after browning.
Remove toothpicks, let rest 5 minutes (the butter will be very hot), then serve whole or sliced to reveal the melted herby center.
