In a pan add butter, then add garlic and sauté it for a minute. Then add mushrooms and cook for 1 to 2 minutes on medium low flame. Now add milk, black pepper, salt, demi-glace powder, oregano and cook for 1 or 2 minutes. Add 7up, mix it well and cook for 2 to 3 minutes. Lastly add cream; mix it well and cook for 4 to 5 minutes or until you reach your desired consistency.Your mushroom sauce is ready. Set aside.