Season both sides of the filets with salt and pepper. Place the filets on the grill at a 45 degree angle to establish good grill marks. Once the filet reaches an internal temperature of 125 to 130 degrees for medium-rare, remove the steak from the grill and let rest about 5 minutes before serving.

For the sauce:

In a saucepan over medium heat, saute mushrooms, shallots, and peppercorns in oil. When shallots are tender, deglaze with red wine and reduce by two-thirds. Whisk together the reduction and demi-glace until smooth. Whisk in the cream and beef base. Combine a few teaspoons of cornstarch (or more as needed) with a little cold water to make a slurry. Add slurry to the sauce to thicken; cook for 1 minute and then remove from the heat.