Line an 8x8 baking pan with parchment paper or aluminum foil, making sure to leave some overhang for easy removal. Lightly grease the bottom and sides and set aside.
In a large microwave safe bowl, melt the butter in the microwave. Add the chocolate chips and sweetened condensed milk. Stir until combined. Place the bowl in the microwave and heat for 1 minute on high. Remove from microwave and stir to combine. If needed, heat an additional 15-30 seconds. Stir until chips are completely melted and chocolate is smooth. Stir in the vanilla extract and chopped pretzels.
Put the caramels and heavy cream in a large microwave safe bowl. Microwave in 20-30 second increments, stirring well after each increment, until the caramel is melted and smooth. Stir in 1/4 teaspoon sea salt.
Add half of the fudge to the prepared baking pan and smooth it out with a spatula. Add the caramel and spread evenly over the fudge with a spatula. Add the remaining half of the fudge and spread it out evenly over the caramel. Top with pretzels and a sprinkling of sea salt.
Place the fudge in the refrigerator for 3-4 hours or until the fudge is solid enough to cut into squares. I like to chill it overnight. Cut the fudge with a hot wet knife. Fudge will keep in the refrigerator for up to 2 weeks.