1 bag (12 oz) semi-sweet chocolate chips
1 tsp vanilla
1 cup mini marshmallows
Use a paper towel to grease an 8x8x2-inch pan with butter -- all over the sides and bottom. Set aside. Combine the sweetened condensed milk and chocolate chips in a saucepan. Heat the mixture over low heat, stirring constantly, until the chocolate is completely melted. Once the mixture is smooth, remove the pan from the heat. Stir in the vanilla extract until completely combined. Add the marshmallows and stir just enough to envelope them in the fudge mixture -- but don't overstir, the marshmallows will melt in if you stir too long. Pour the fudge into the prepared pan and smooth the top slightly. Refrigerate to set, 1 1/2 hours or longer. Once set, cut into 1-inch squares.