Prep the chicken: Butterfly each chicken breast by slicing horizontally almost to the edge, then open like a book. Gently pound to an even 1/4–1/2 inch thickness between plastic wrap.

Season and spread: Pat the chicken dry and season both sides with salt and pepper. Smear about 1/2 teaspoon Dijon inside each breast.

Assemble the pockets: Place 2–3 thin apple slices on one side of each butterflied breast, top with 1–2 slices of brie and a sprinkle of thyme and minced garlic. Fold closed and secure with toothpicks or twine.

Coat the outside (optional): If using panko, brush the outside lightly with olive oil and press panko onto the chicken. If skipping crumbs, lightly dust with salt and pepper.

Sear the chicken: Heat 2 tablespoons olive oil and 1 tablespoon butter in a large ovenproof skillet over medium-high heat. Add chicken, seam-side down first, and sear 3–4 minutes per side until golden brown.

Finish in the oven: Transfer the skillet to a 375°F (190°C) oven and roast 10–12 minutes, or until an instant-read thermometer reads 160°F (71°C) at the thickest part.

Make the pan sauce: Remove chicken to rest. Place skillet over medium heat, add wine or broth and scrape up browned bits. Simmer 2–3 minutes; whisk in cornstarch slurry if you want a thicker sauce and simmer until glossy.

Serve: Remove toothpicks, slice each breast at a slight angle to reveal the melty filling, and spoon pan sauce over top. Garnish with extra thyme and thin apple slices.