Step 1

Line a baking sheet with parchment paper; set aside. Finely chop 1/2 cup toasted pecans, leaving the remaining 1 1/2 cups whole.

Step 2

In a medium saucepan, stir together brown sugar, condensed milk, corn syrup, butter, and salt. Place over medium heat and bring to a boil, stirring constantly, until mixture reaches 240°F, about 5 minutes. Remove from heat; stir in vanilla extract and baking soda.

Step 3

Add chopped and whole pecan halves and stir for one minute until caramel begins to thicken slightly. Working quickly, use a spoon to scoop 2 tablespoons of mixture in a mound on prepared baking sheet. Repeat until all of the mixture has been used, yielding 12 caramel-pecan mounds. Transfer baking sheet to refrigerator until mounds have solidified and are no longer warm to the touch, about 20 minutes.

Step 4

Over a double boiler or in the microwave, melt chocolate until smooth. Coat each caramel mound in chocolate, gently lifting the mound out of the chocolate with a fork allowing excess chocolate to drip off. Return chocolate covered mound to its place on baking sheet. If using, sprinkle surface with flake salt while chocolate is still warm. Repeat with remaining mounds, chocolate, and flake salt. Once all turtles are coated, return baking sheet to refrigerator to allow chocolate to harden, about 30 minutes. Store in an airtight container and keep in the fridge.