Prepare baking pan: Line an 8-inch square baking pan with parchment paper, leaving a 2-inch overhang on all sides. Lightly coat pan with cooking spray; set aside.
Combine fudge ingredients and heat: Cook condensed milk, chocolate chips, and salt in a medium saucepan over medium-low, stirring constantly, until chocolate is melted and mixture is glossy and thick, 5 to 6 minutes. Remove from heat, and quickly stir in vanilla until combined.
Add fudge mixture to pan: Pour chocolate mixture into prepared pan; smooth top using a small offset spatula. Refrigerate uncovered until firm, at least 2 hours or up to 12 hours.
Cut fudge: Remove from pan using parchment paper overhang as handles. Cut into 64 (about 1-inch) squares.
