Combine the 3 cups milk chocolate chips and the 1 (14-ounce) can sweetened condensed milk in a microwave-safe bowl. Stir together and microwave for 30 seconds and stir well.
Microwave the fudge mixture in bursts of 15 seconds stirring for 30 seconds in between until completely melted. Stir in the 2 teaspoons vanilla extract.
Pour the fudge mixture into the prepared pan. Spray a spatula with nonstick cooking spray and smooth the fudge.
In a separate bowl, combine the 25 soft caramels, and 2 tablespoons heavy cream. Microwave for 30 seconds then stir for 30 seconds.
Return the mixture to the microwave and microwave in bursts of 15 seconds stirring for 30 seconds in between until completely melted. Pour the caramel over the chocolate evenly.
If desired top the fudge pieces with sea salt. Cover tightly and place in the fridge to harden/set up overnight.
Cut the fudge with a hot wet knife. Store any leftover fudge in an airtight container in the fridge.