Step 1: Prepare the Pan: Line an 8x8 inch baking pan with parchment paper, leaving an overhang on two sides. This will make it easy to remove the fudge later.
Step 2: Melt the Chocolate: In a medium saucepan over low heat, combine the sweetened condensed milk and chocolate chips. Stir constantly until the chocolate is completely melted and the mixture is smooth. Be careful not to overheat the chocolate, as it can scorch easily. Alternatively, melt the chocolate and sweetened condensed milk in the microwave in 30-second intervals, stirring well between each interval, until smooth.
Step 3: Add Flavorings: Remove the saucepan from the heat and stir in the vanilla extract and chopped walnuts (if using). Ensure everything is well combined.
Step 4: Transfer to Pan: Pour the chocolate mixture into the prepared baking pan, spreading it evenly with a spatula.
Step 5: Chill Until Set: Cover the pan with plastic wrap and refrigerate for at least 2 hours, or until the fudge is firm.
Step 6: Cut into Bars: Once the fudge is set, use the parchment paper overhang to lift it out of the pan. Place the fudge on a cutting board and use a sharp knife to cut it into 16 equal-sized bars.
For a twist, try using different types of chocolate chips, such as milk chocolate or dark chocolate. Other nuts like pecans or almonds can be substituted for walnuts. A pinch of sea salt sprinkled on top before chilling enhances the flavor.