In a medium skillet, melt butter over medium heat. Add shallots, and cook until translucent. Add wine, and cook until liquid has evaporated, about 5 minutes. Add glace de viande and stock. Bring to a boil. Reduce to a simmer.
Meanwhile, in a small bowl, dissolve cornstarch in heavy cream. Whisk into sauce, and cook, stirring, until sauce thickens, about 2 minutes. Season with salt and pepper.
Remove from heat, and pass through a sieve. Keep warm in a double boiler, or a heatproof bowl set over a pan of simmering water.