1. Line an 8×8 pan with parchment paper.
2. In a large saucepan over medium heat, combine the milk and dark chocolate chips with 1 cup of the sweetened condensed milk. Stir while the chocolate melts until you have a smooth mixture, about 5-10 mins. Remove from the burner and add the marshmallow cream and vanilla. Pour 1/2 of the fudge into the baking pan and set aside the rest for later.
3. Sprinkle 1 cup of the pecans evenly across the top of the fudge and lightly press them into the chocolate so they will stick.
4. Place pan in refrigerator to set up, about an hour or fifteen minutes in the freezer.
5. In a microwave-safe bowl, combine the unwrapped caramels and the ¼ cup of remaining sweetened condensed milk. Microwave until melted and smooth, 1-2 minutes. Pour the caramel evenly over your fudge layer, reserving 2 tablespoons for drizzling on top. Place in freezer for 15 mins to set up.
6. Re-heat the remaining half of the chocolate fudge over low heat and stir until smooth again. Spread it over caramel layer.
7. Re-melt the reserved caramel and drizzle it over the top of your fudge. Sprinkle with flaky sea salt if desired.
8. Refrigerate for at least 2-3 hours before cutting, slice into even squares and devour immediately.