Cook bacon or pancetta at medium heat for about 3 min.
Add 1 T olive oil, mushrooms, garlic and thyme to the pan.
Cook on medium heat for about 5 min, stirring, until mushrooms soften and release juices. Sprinkle 2 T flour all over the mushrooms, and stir the flour in on medium heat.
Add cream and demi-glace and raise the heat to bring to boil, stirring constantly. Reduce heat to low. Remove thyme.