Preheat the oven to 400°F (200°C).
Season the turkey breast evenly with salt and black pepper.
Heat olive oil in a skillet over medium-high heat. Sear the turkey breast for 2-3 minutes on each side until golden brown. Remove from heat and let cool slightly.
In the same skillet, add butter, chopped mushrooms, shallots, and garlic. Cook over medium heat for 6-8 minutes until the mixture is soft and most of the moisture has evaporated.
Stir in dried thyme and dried sage, cook for an additional 1 minute. Remove from heat and let cool completely to form the mushroom duxelles.
On a lightly floured surface, roll out the puff pastry sheet to a 10×10 inch square.
Spread the mushroom duxelles evenly in the center of the pastry, leaving a 1-inch border around the edges.
Place the seared turkey breast on top of the mushroom mixture.
Spread the prepared bread stuffing evenly over the turkey breast.
Top the stuffing with cranberry sauce, spreading gently.
Carefully fold the puff pastry edges over the filling to completely enclose it, sealing the edges by pressing gently with your fingers or a fork.
Place the wrapped Wellington seam side down on a baking sheet lined with parchment paper.
Brush the entire pastry surface with the beaten egg to achieve a golden finish.
Using a sharp knife, lightly score the top of the pastry with a decorative pattern if desired, being careful not to cut through.
Bake in the preheated oven for 40-45 minutes, or until the pastry is golden brown and cooked through.
Remove from the oven and let rest for 10 minutes before slicing and serving.