In a large heavy-bottomed saucepan on medium heat, combine cream, brown sugar, corn syrup, butter, and salt. Stir constantly as the butter melts and sugar dissolves. The mixture will be thick, cloudy, and dull-looking.

Once the butter is completely melted, stop stirring and bring the mixture to a boil. Brush down the side of the pan with a water-moistened pastry brush.

Cook until the caramel reaches 235 F (soft ball stage) on a candy thermometer. When it hits that stage, begin stirring lightly, once every minute. If any candy splashes up the side of the pan, brush it off with a water-moistened pastry brush. The caramel will be begin to thicken. As soon as the caramel reaches 250 F (hard ball stage), remove the pan from the heat and immediately stir in the vanilla extract.

While caramel cooks slightly, line two large baking sheets with parchment paper or silicone baking mats. Arrange 48 clusters of four pecan halves each, leaving one inch of space between the clusters.

Spoon two teaspoons of the caramel onto the center of each pecan cluster. Let the caramel cool completely to room temperature, about 30 minutes.

Temper the chocolate (see how to temper chocolate for instructions), and spoon one teaspoon of chocolate over the caramel on each turtle. Allow the chocolate to completely set at room temperature (about 45 minutes).