Line an 8×8-inch pan with foil and spray with nonstick spray.
Combine chocolate chips, sweetened condensed milk, and butter in a medium saucepan.
Cook over low heat for 5 minutes, stirring constantly, until chocolate is melted.
Remove from heat and stir in vanilla extract and salt.
Pour mixture into prepared pan.
Refrigerate about 2 hours or until set.
Lift foil to remove fudge and cut into 1-inch squares.
Notes
Line the pan well and spray under the foil to prevent sticking.Use medium-low heat to avoid scorching the chocolate.Store fudge in an airtight container in the refrigerator up to 1 week.