Line an 8 or 9-inch square baking pan with parchment paper, leaving enough overhang for pan removal later; set aside
In a small microwaveable bowl, heat peanut butter for thirty seconds on high heat; stir in powdered sugar; set aside
Place chocolate chips and sweetened condensed milk in a large microwaveable bowl; heat for thirty seconds on high and stir; repeat once or twice until chocolate is completely melted and mixture is smooth (it will get thick quickly); immediately spread in prepared baking pan
Spoon peanut butter mixture over chocolate and use a knife to swirl peanut butter into chocolate; sprinkle lightly with sea salt if desired
Chill pan in freezer for thirty minutes or fridge for one hour; once chilled, remove fudge from pan by using sides of parchment paper to lift it up; place on a cutting board and slice
Serve immediately or store leftovers in fridge for up to a week
Notes
Notes: Recipe from Five-Ingredient Recipes, A Cookbook for Busy People
Recipe by Keep It Sweet Desserts at http://www.keepitsweetdesserts.com/chocolate-peanut-butter-swirl-fudge/