Season the chicken
Season both sides of the chicken breasts evenly with salt, dried thyme, and black pepper. Set aside while you prepare the filling.

Create the pocket
Using a sharp knife, carefully slice each chicken breast lengthwise to create a deep pocket. Avoid cutting all the way through so the filling stays inside during cooking.

Sauté the spinach
Heat 1 tablespoon of olive oil in a medium pan over medium heat. Add the diced shallot and garlic and cook for about 30 seconds, until fragrant. Add the spinach and cook for 1–2 minutes, stirring often, until just wilted. Remove from heat.

Stuff the chicken
Spoon about 2 tablespoons of cranberry sauce into each chicken pocket. Divide the spinach mixture evenly between the chicken breasts, then top each with slices of brie cheese. Secure the opening with 3–4 toothpicks.

Sear the chicken
Preheat the oven to 400°F (200°C). Heat the remaining 2 tablespoons of olive oil in a large oven-safe skillet over medium heat. Sear the stuffed chicken breasts for about 3 minutes per side, until golden brown.

Bake until done
Transfer the skillet to the oven and bake for 15–18 minutes, or until the chicken reaches an internal temperature of 165°F (73°C).

Rest and serve
Remove the chicken from the oven and let it rest for a few minutes before serving. This allows the juices to redistribute and keeps the chicken moist.