Grilled Filet Mignon with Red Wine Sauce

I make this recipe frequently it's one of my favorites.
The left overs freeze well if there ever are any!

Ingredients:
6 (4 to 6-ounce) filet mignons
Kosher salt and freshly ground black pepper
3 tablespoons extra-virgin olive oil
6 tablespoons cold unsalted butter
1 onion, peeled and thinly sliced
1 tablespoon minced garlic
1 teaspoon dried oregano
1/4 cup tomato paste
2 1/2 cups dry red wine

Directions:
Preheat grill to medium-high heat.
Generously season the steaks with salt and pepper
and drizzle with the 3 tablespoons of olive oil.
Grill to desired doneness, about 5 minutes per side for medium-rare. Transfer the steaks to a cutting board.
Tent with foil and let stand 10 minutes.
Meanwhile, melt 2 tablespoons of butter in a
heavy large saucepan over medium-high heat.
Add the onions and saute until tender, about 5 minutes. Season with salt. Add the garlic and oregano and saute until fragrant, about 30 seconds. Stir in the tomato paste and cook for 2 minutes, stirring constantly. Whisk in the wine. Simmer until the sauce reduces by half,
stirring occasionally, about 10 minutes. Remove the skillet from the heat. Strain the sauce into a small bowl, pressing on the solids
to extract as much liquid as possible. Discard the solids in the strainer and return the sauce to the saucepan and bring back to a slow simmer.
Cut the remaining 4 tablespoons of butter into small 1/2-inch chunks
and whisk in the sauce a little at a time.
Season the sauce, to taste, with salt and pepper.
Place filets on each of 6 dinner plates.
Drizzle the sauce over the filets and serve.