In a large saucepan melt butter, add sliced mushrooms, cook on medium heat for 8-10 minutes mixing often.
3 Tbsp. unsalted butter, 1 lb. white mushrooms
Add vegetable stock, salt, garlic powder and black pepper. Cook covered on low heat for about 3 minutes.
2 cups vegetable stock, 1/2 tsp. salt, 1/4 tsp. garlic powder, 1/8 tsp. black pepper
In a medium jar mix heavy cream with few tablespoons of water base, pour to the sauce, heat it through for 1-2 minutes.
1/2 cup heavy cream
In a small bowl make a slurry with cornstarch and water. Add to the sauce. Whisk it until thickens. Turn off the heat.
2 Tbsp. cornstarch, 2 Tbsp. water