Line an 8” square baking pan with foil or parchment paper.

Spread 1 cup of mini-marshmallows evenly across bottom of pan; set pan aside.

Using a medium saucepan, add chocolate chips and sweetened condensed milk. Cook over low heat, stirring often, until smooth. Remove pan from heat and stir in chopped peanuts, remaining 2 cups of mini-marshmallows and vanilla extract.

Pour mixture into prepared baking pan, using a spatula to help spread mixture evenly.

Heat marshmallow fluff in a microwavable bowl until soft (~15-20 seconds).

Using a table knife, swirl the marshmallow fluff into the melted chocolate mixture.

Refrigerate for 2 hours, or until firm.

Remove from pan; discard parchment/foil. Slice into 36 pieces.