Creating Christmas Stuffed Beef Tenderloin is a straightforward process if you follow these simple steps:

1. Prepare the Stuffing: In a skillet, heat olive oil over medium heat. Add onions and garlic, sauté until translucent.
2. Add Spinach and Mushrooms: Stir in the chopped spinach and mushrooms. Cook until the moisture evaporates. Remove from heat and let cool slightly.
3. Combine Ingredients: In a large bowl, combine breadcrumbs, cooked spinach mixture, thyme, rosemary, salt, pepper, Parmesan cheese, and beaten eggs. Mix well to create the stuffing.
4. Prepare the Beef: Lay the beef tenderloin on a cutting board. Using a sharp knife, slice the tenderloin lengthwise, being careful not to cut all the way through. Open it like a book.
5. Fill the Tenderloin: Spread the stuffing evenly over the opened tenderloin. Roll it up tightly, starting from one end to the other.
6. Tie the Roast: Use kitchen twine to tie the roast securely, ensuring the stuffing stays inside.
7. Preheat Oven: Preheat your oven to 375°F (190°C).
8. Sear the Beef: In a large oven-safe skillet, heat a little olive oil over medium-high heat. Sear the beef on all sides until browned (about 4-5 minutes per side).
9. Roast in Oven: Transfer the skillet to the preheated oven and roast for about 1 hour, or until the internal temperature reaches 135°F (57°C) for medium-rare.
10. Rest the Meat: Remove the beef from the oven, cover with foil, and let it rest for 30 minutes before slicing.

These steps will guide you in creating this incredible dish effortlessly, ensuring a flavorful experience for you and your guests.