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
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.