Step 1: Prepare Your Pan - Line a 9x9 inch baking pan with parchment paper, allowing some overhang on the sides.
Step 2: Melt the Chocolate - In a microwave-safe bowl, combine 3 cups of semi-sweet chocolate chips and the can of sweetened condensed milk. Microwave in 30-second increments, stirring in between, until completely melted and smooth.
Step 3: Mix in the Peanut Butter and Vanilla - Add the creamy peanut butter, dash of salt, and vanilla to the melted chocolate mixture. Stir until well combined and creamy.
Step 4: Fold in the Mini Peanut Butter Cups - Gently fold in 1 cup of chopped mini peanut butter cups and 1/2 cup of peanut butter chips into the chocolate mixture.
Step 5: Pour and Spread - Pour the fudge mixture into the prepared baking pan, using a spatula to spread it evenly.
Step 6: Top with Chocolate Chips - Sprinkle 1/2 cup of semi-sweet chocolate chips on top of the fudge. Gently press them into the surface.
Step 7: Chill - Refrigerate the fudge for at least 2 hours, or until it has completely set.
Step 8: Cut and Serve - Once set, lift the fudge out of the pan using the parchment paper overhang. Cut into squares and serve.