Pauline Trigère’s Mushroom Spaghetti

Cut the onions into very thin slices. Melt half of the butter in a heavy skillet and add the onions. Cook, stirring, until the onions have a delicate brown color.

Cover the skillet and cook the onions for one hour over very low heat. Stir occasionally.

In a second skillet melt the remaining butter and sauté the mushrooms in it unt