Prepare an 8x8" pan by spraying with cooking spray and laying a piece of wax paper inside the pan with edges hanging out.

Chop up chocolate finely and place in a large bowl. Melt in the microwave at 1 min. intervals stirring in between until almost melted. Stir at the end to finish melting and to make sure it is smooth. Add the marshmallows and nuts and stir to combine.

Pour into prepared pan and refrigerate until set. Lift out of the pan using the wax paper. Cut into 1" squares. Store in a container in the refrigerator.