Butter a square pan and line with parchment paper for easy removal of set fudge. Set aside. In a microwave safe 2 quart bowl, heat chocolate chips and sweetened condensed milk, on high for 1 minute. Remove from microwave. Let sit for 1 minute, then stir to combine. If needed, heat an additional 30 seconds. Stir until chips are completely melted and chocolate is smooth. Stir in vanilla extract. Pour fudge into prepared pan. Let fudge cool completely before cutting into 1 inch squares. (you can place in the refrigerator for 1 hour to speed up the process.) Store in an airtight container. Fudge does not need to be kept refrigerated.