Heat the oil in a medium saucepan. Add the shallots, mushrooms and thyme and cook over high heat for 10 minutes, stirring frequently. Add the stock and boil until the mushrooms are almost dry. Stir in the wine and boil until reduced to 2 tablespoons, about 30 minutes. Stir in the cream and bring to a boil over low heat. Whisk in the butter and sugar and season with salt and pepper. Strain the sauce through a fine sieve, pressing on the solids, and keep warm.