Heat 1 tablespoon of olive oil in a large skillet over medium heat. Add diced shallots and cook for 2 minutes until softened. Add minced garlic and cook for 30 seconds until fragrant. Add the chopped spinach and cook for 3-4 minutes, stirring frequently, until the spinach is wilted and any excess moisture has evaporated. Season with a pinch of salt and pepper. Remove from heat and let cool slightly, then fold in the dried cranberries and set aside.

Place each chicken breast on a cutting board. Using a sharp knife, carefully cut horizontally through the thickest part of each breast, creating a pocket without cutting all the way through. Be gentle to avoid cutting through the sides. Pat the chicken dry with paper towels.

Divide the spinach-cranberry mixture evenly among the four chicken breasts, placing it inside each pocket. Top each portion of filling with 1.5 ounces of brie cheese. Don't overstuff; leave enough room for the filling to stay contained during cooking.

Season the outside of each stuffed chicken breast generously with salt, pepper, and any additional herbs you prefer. This step is crucial for developing a flavorful crust.

Heat 2 tablespoons of olive oil in a large ovenproof skillet over medium-high heat. Once the oil is shimmering, carefully place the stuffed chicken breasts in the skillet. Sear for 4-5 minutes on the first side without moving them, until golden brown. Flip gently and sear the other side for another 3-4 minutes.

Pour the chicken broth (and white wine if using) around the chicken breasts. Add fresh thyme or rosemary sprigs to the pan. The liquid should come about one-third of the way up the sides of the chicken.

Transfer the skillet to a preheated 375°F (190°C) oven. Bake for 12-15 minutes, until the chicken reaches an internal temperature of 165°F (74°C) when measured with a meat thermometer inserted into the thickest part of the breast.

Remove the skillet from the oven and let the chicken rest for 5 minutes before serving. This allows the juices to redistribute throughout the meat, keeping it moist and tender. Spoon any pan juices over the chicken before plating.