Start out by placing the top oven rack in the center position.
Then pre-heat the oven to 400°F. (yes that is the correct temperature)
Prep your roasting pan by placing the red onions below the rack (if you are using red onions, you can eliminate them as well!)
For The Stuffing
Next, heat 2 of the 4 tablespoons of olive oil in a large, rimmed skillet.
Keep this skill on medium heat, not high.
Place in the skillet (Pan) leeks, mushrooms, and garlic.
Don't forget to season them with a good dash of salt and black pepper, to taste.
Last stir what you have in that pan!
Cook, stirring occasionally until the vegetables develop some color.
What actually will happen is that the water that the mushrooms leak will evaporate and that is key to knowing that it is time to move to the next step. (about 8-12 minutes)
Now it is time to add to the mixtures: spinach and fresh herbs.
The next part is about spinach wilting.
That's a fast time overall about 2 minutes.
Continue cooking until the spinach wilts, approximately 1-2 minutes. Remove from heat and set aside.
STUFFING THE TENDERLOIN
Set the butterflied beef tenderloin between two sheets of parchment paper, and use a meat mallet or a rolling pin to achieve a uniform thickness of 1/2".
Once that is met, brush the surface of the beef with the remaining olive oil (2 Tablespoons) and again you will use freshly milled salt and pepper to graciously season to taste.
Next, you will add the Parmesan cheese into the mushroom-spinach mixture until combined.
Then you are going to fill the butterflied tenderloin.
Taking care to evenly spread the mixture over the beef tenderloin.
**NOTE*** DO leave a small border (½-1 inch) around the edges or the content inside will be blowing out the sides!
Start at one end of the roast, and begin to roll it.
There's no good way to explain this, just work on the end you are happiest with!
roll up the tenderloin as though you are rolling a jelly roll.
You'll want to then tie each section off as you go with twine (butchers thread).
Do season the outside of the beef with salt and pepper if you desire and of course, you can also toss more of the fresh herbs atop!
Make certain to place the roast in the center of a roasting pan lined with the sliced red onions.
(if you hate red onions skip them as stated above or use sweet yellow onions!)
You will want to nestle the shallots and carrots and potatoes around the beef.
Then tuck in the fresh thyme sprigs.
For the last item, you will add in the beef broth.
Place the meat into the oven, and roast the meat, until the beef reads
... between 125°F-130°F* for medium-rare on an instant-read thermometer.
Pretty much this will happen in about 35-40 minutes.
While the meat rests, you will note that the thermometer may rise another 5 degrees or so.
The veggies may not be done, so take a fork to them and test.
If they are not done, return them to the oven while the meat rests for about 15 minutes or of course you could microwave them for 8 or so!
Once you are ready to serve the meat, transfer the beef tenderloin to a serving platter.
You'll want to loosely cover it with foil to keep it warm.
GRAVY
Now it's time to take the pan juices out and make them into a lovely thick sauce.
Take the pan juices and transfer them into a medium saucepan.
Place over medium-high heat and reduce for approximately 5 minutes, stirring occasionally.
Add the butter and stir to emulsify the butter and thicken the sauce.
Carve the stuffed tenderloin and serve immediately with the roasted vegetables and pan sauce.
Enjoy! ~ Dana xo
