04In 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.