Line a loaf pan with parchment paper. I used a box lid measuring 6 x 9 inches.

In a large microwave-safe bowl, combine chocolate chips, butter, and sweetened condensed milk. Microwave on high power for 1 ½ - 2 minutes, stirring every 30 seconds until all melted. Don’t cook any longer than necessary.

Mix in vanilla extract and walnuts.

Spread into prepared pan, and refrigerate 2-3 hours, until set. Cut into squares, and store in airtight container, in the fridge.