Place 2 Tbsp. jarred caramel topping in the bottom of each of 4 chilled glasses, and sprinkle with 1/4 tsp. flaky sea salt. Process vanilla ice cream, butter-pecan ice cream, and milk in a blender until foamy and thick, 3 to 4 minutes. Divide milk shake evenly among prepared glasses; top with whipped cream, and drizzle each with 1 Tbsp. caramel topping. Sprinkle each with 1/4 tsp. flaky sea salt, and top with 1 Tbsp. chopped toasted pecans. Serve immediately.