Add semisweet chocolate chips, 1 1/2 cups andes mint chips, sweetened condensed milk, and butter to a large microwavable bowl. Place in the microwave for 30 seconds at a time mixing between until fully melted. This could have 2-3 minutes to cook.
Once everything is melted mix until well combined. Pour these ingredients into a 8x8 casserole dish (I used parchment paper for easy removal).
Top with reaming 1/2 cup of andes mint chips. Allow to set for several minutes to melt and use a knife to swirl in melted andes mint chip topping.
Place in the fridge until set. This will take at least 2 hours. Then slice into fudge pieces and enjoy!