Line a 9x9 inch baking pan with parchment paper, allowing some overhang on the sides for easy removal later.
In a microwave-safe bowl, combine the chocolate chips and peanut butter. Microwave in 30-second intervals, stirring between each, until completely melted and smooth.
Once melted, fold in any optional mix-ins like chopped walnuts, shredded coconut, or chia seeds.
Pour the fudge mixture into the prepared baking pan and spread it evenly with a spatula.
Place the pan in the refrigerator for at least 2 hours, or until the fudge is firm enough to slice into bars.
Lift the fudge out of the pan using the parchment overhang, slice into bars or squares, and enjoy!
