Line 8 x 8 inch pan with parchment paper leaving an overhang. You will use this overhang to help remove the fudge from the pan.
In large microwavable bowl add chocolate chips, sweetened condensed milk and butter. Cook in microwave at 50% power until chips are melted; approximately 3-5 minutes. Stir a couple of times during the cooking process. After chips are melted quickly stir in mini marshmallows and pecans.
Pour into parchment lined pan and smooth with the back side of a spoon lightly sprayed with nonstick baking spray. Refrigerate until set. Using the overhang lift fudge out of pan and place on cutting board or plate. Peel off parchment paper and cut into bite size pieces.