Place chocolate chips, sweetened condensed milk, and butter or margarine in large microwaveable bowl. Zap in microwave on medium until chips are melted, about 3-5 minute, stirring once or twice during cooking. Stir in nuts, if desired.
From AllRecipes.com
http://allrecipes.com/recipe/fudge/detail.aspx?event8=1&prop24=SR_Title&e11=fudge&e8=Quick%20Search&event10=1&e7=Home%20Page
Pour into well-greased 8x8-inch glass baking dish. Refrigerate until set.