Step 1

Line an 8x8 baking dish with parchment paper and set aside.

Step 2

Add chocolate chips, sweetened condensed milk, salt, and espresso powder (if using) to a medium heavy-bottomed saucepan over medium-low heat. Melt the chocolate, stirring frequently. Remove from heat and stir in vanilla extract. Stir in any optional mix-ins if using. (see fudge flavor variations in note)

Step 3

Pour the mixture into the prepared pan and spread with an offset spatula or a rubber scraper if needed. Cover with plastic wrap and refrigerate for 2 hours to set. Remove from refrigerator and remove from baking dish. Cut into 24 or 48 individual squares.

Step 4

Add chocolate chips and sweetened condensed milk to a large microwave-safe bowl. Heat at 30-second increments, stirring after each, until the fudge mixture is melted, smooth, and creamy. Stir in any optional mix-ins if using. (see fudge flavor variations in note)

Step 5

Pour into prepared baking dish and spread with an offset spatula or a rubber scraper if needed. Cover with plastic wrap and refrigerate for 2 hours to set. Remove from refrigerator and remove from baking dish. Cut into 24 or 48 individual squares.