Butter a square pan and line with wax paper. Set aside.
Place chocolate chips and sweetened condensed milk in a microwave safe bowl and heat on high for 1 minute.
Remove from microwave, let sit for 1 minute, then stir until chips are completely melted and chocolate is smooth. You may need to heat for additional 30 seconds.
Optional - Stir in extract of choice (vanilla, almond etc).
Pour fudge into prepared pan. Let fudge cool completely before cutting into squares.
Store in an airtight container, no need to keep refrigerated.