Mushroom sauce

I made this on the fly halfway through the cooking process. Originally, my plan was to just saute some sliced white mushroom in butter and garlic, and just call it a day. I had covered the mushroom to wilt down and got the idea to make a gravy with it when I saw all the wonderful liquid that had come out after uncovering. I melted down another pat of butter in the center of the mushroom pile then about a tablespoon of flour to make a roux, then just added water to the mixture until I got my desired amount of sauce. Season with salt and pepper before serving. SO EASY! We had this with steak and potatoes.