01 -
Place the chocolate chips, sweetened condensed milk, and butter in a large, microwave-safe mixing bowl.
02 -
Microwave the bowl on high power for 1 minute. Remove and immediately stir the ingredients together until smooth and homogenous.
03 -
Stir in the vanilla extract and chopped nuts, if using, until evenly distributed.
04 -
Transfer the mixture into a greased 20 x 20 cm pan. Spread evenly with a spatula.
05 -
Refrigerate for at least 2 hours until firm throughout.
06 -
Cut into 16 squares and serve as desired.